(19) European Patent Office

Description

[0001] The invention relates to a method for determining the angle of the relative alignment of an antenna array of a radio station as well as to a respective radio system and a respective radio station.

[0002] In radio systems, such as those of the mobile radio, it is possible to use directional antennas. In contrast to omni-directional antennas, said directional antennas do not emit their signals at all four cardinal compass points, but rather only in adjustable directions. Directional antennas may be implemented by means of antenna arrays. An antenna array is formed by at least two antennas, but typically by more than two antennas, which are aligned in relation to each other in such a manner that on simultaneous transmission of the signals over all antennas of the antenna array the desired characteristic of the directional antenna is achieved.

[0003] Cellular mobile radio systems use a large number of base stations. There exist systems with many thousands of base stations. The base stations are controlled by central units of the mobile radio network - for exammple, base station controllers. If the base stations are equipped with directional antennas, it is necessary for the central units to know the alignment of the directional antennas and/or the antenna arrays of each base station. Only if this knowledge is on hand, is it possible for the central units to control and/or monitor the resources used by the individual base stations. For this reason when a mobile radio system is installed, the directional antennas of the base stations are aligned in a defined way that is known to the central units. External influences, such as storms, often result in the antennas, which are initially aligned in a correct way being shifted out of their alignment. The mobile radio network remains unaware of this misadjustment until a person visits the base station in question and checks the alignment of the antenna array. Traditionally a compass is used to perform this check.

[0004] The object of the invention is to simplify the process of determining the alignment of an antenna array and/or a directional antenna.

[0005] This object is achieved with the method, disclosed in claim 1, as well as a radio system, disclosed in claim 10, as well as a radio station, discclsoed in claim 10. Advantageous embodiments and further developments of the invention are the subject matter of the dependent claims.

[0006] In the case of the inventive method for determining the angle of the relative alignment of an antenna array of a first radio station, which exhibits at least two antennas, relative to a reference direction, the angle of a directional vector between the first radio station and a second radio station relative to the reference direction is determined. Signals are transmitted from the second radio station to the first radio station; and these signals are receved by the antenna array of the first radio station. Then a reception angle between the received signals and the alignment of the antenna array is determined. Then the angle of the alignment of the antenna array relative to the reference direction is determined as the difference between the angle of the directional vector and the reception angle.

[0007] The invention provides an advantageous way of determining automatically the alignment of the antenna array without the need for the service personnel to visit the first radio station. The described process steps may be carried out in that namely the first radio station totally utilizes the signals of the second radio station.

[0008] According to a further development of the invention it is then possible to transmit the angle of the alignment of the antenna array (after it has been determined in the first radio station) to a central unit, which is connected to several radio stations. Then, if each of the radio stations carries out the inventive method, the central unit then has the information about the alignment of the directional antennas of all of these radio stations.

[0009] The directional vector, which is used for determining the relative alignment, can be easily determined from the geographical positions of both radio stations. If the radio stations are stationary stations, then their positions can be determined at the time of their installation and stored, for example, permanently in the first radio station. However, a further development of the invention also makes it possible to determine the geographical positions of the radio stations with the aid of a radio-assisted positioning system. This strategy also makes it possible at a later date to update the information about the positions of the radio stations and is especially practical when the radio stations are mobile.

[0010] According to one advantageous alternative of the invention, the first radio station does not perform the task of totally determining the alignment of the antenna array. Rather only the reception angle between the received signals and the alignment of the antenna array is determined by the first radio station and optionally transmitted to a central unit, which is connected to several radio stations. In contrast, the angle of the directional vector between the first radio station and the second radio station and/or the difference between the anlge fo the directional vector and the reception angle is determined by the central unit. If only the angle of the directional vector is determined by the cetnral unit, then this unit has to transmit the determined value to the first radio station, so that this first radio station can then compute the angle of the relative alignment of its antenna array. However, it is also possible for the first radio station to calculate the angle of the directional vector (for example, on the basis of the information about the positions of the first and the second radio station that it has obtained from the central unit) and then to send this value together with the reception angle between the received signals and the alignment of the antenna array to the central unit, where then the difference between the angle of the directional vecotgr and the reception vector is determined.

[0011] According to an advantageous further develpment of the invention, the following steps are taken for an additional determination of the relative position of a third radio station.

[0012] The signals, which are emitted from the third radio station, are received by the first radio station; and a recption angle between these received signals and the alignment of the antenna array of the first radio station is determined. Then the relative position of the third radio staion is determined as the difference between the angle of the alignment of the antenna array of the fist radio station relative to the reference direction and the reception angle of the singals of the third radio station. In this way the relative position of the third radio station in relation to the first radio station can be dtermined in an advantageous way.

[0013] According to one embodiment of the invention, the first and the second radio station are stationary stations - for example, base stations in a mobile radio system -; and the third radio station is a mobile station.

[0014] The invention is suited for use in any radio system, in particular any mobile radio system, insofar as only directional antennas and/or antenna arrays are used.

[0015] The inventive radio ssytem and the inventive radio station exhibit means and/or device that are used for carrying out the method of the invention.

[0016] The invention is explained in detail below with reference to the embodiments depicted in the figures.

[0017]

Figure 1 depicts two adjacent radio cells of a mobile radio system.

Figure 2 depicts the detailed procedure for determining the alignment of an antenna array of a radio station from Figure 1; and

Figure 3 depicts an radio station of the invention.

[0018] Figure 1 depicts a detail of the inventive radio system in the form of a cellular mobile radio system. The mobile radio system may be, for example, one in accordance with the global system for mobile communications (abbr. GSM) standard or the universal mobile telecommunications system (abbr. UMTS) standard. Depicted are two radio cells C1, C2, to which a base station BS1, BS2 is assigned in each case. Each base station exhibits an antenna array A1, A2. In the illustrated embodiment each antenna array has only two antennas. In practice a larger number of antennas may be used. The antenna arrays A1, A2 in Figure 1 are directional antennas, which may be used to both receive and to send signals. Both base stations BS1, BS2 are connected to a central unit RNC of the mobile radio network. In the example under discussion this central unit is a base station controller. The second base station BS2 transmits signals S1 to the first base station BS1. Furthermore, Figure 1 shows, as an example, a mobile station MS, which transmits signals S2 to the first base station BS1. The following discussion elucidates how an angle of the relative alignment of the antenna array A1 of the first radio station BS1 is determined.

[0019] Figure 2 depicts the two base stations BS1, BS2 and the mobile station MS in a different presentation, which shows the operands that are required to calculate the alignment of the antenna array A1 of the first base station BS1. It is assumed that the angle alpha 1 of the relative alignment AA1 of the antenna array A1 of the first radio station BS1 relative to a reference direction N is to be determined. The reference direction N may be, as an example, the north direction. It may be determined, for example, with a compass and can also be assumed to be known. The alignment AA1 of the antenna array A1 is produced by the arrangement of the antennas of the antenna array in relation to each other. For the sake of simplification Figure 2 shows the alignment as bars. In a first step the angle gamma of the directional vector V between the first radio station BS1 with the coordinates X1, Y1 and the second radio station BS2 with the coordinates X2, Y2 is determined. To this end the directional vector V is calculated from the coordinates X1, Y1 and X2, Y2.

[0020] The coordinates X1, Y1 or X2, Y2 of the two base stations BS1, BS2 are plotted in Figure 2 and may be determined, for example, with a radio-assisted positioning system, such as GPS. This step can be carried out once and for all during the installation of the mobile radio system and the two base stations BS1, BS2. Then the coordinates that are determined by this method can be stored centrally in the mobile radio network, so that the centarl unit RNC has access to them. In this way it is able to use the coordinates in question for the calculation of the directional vectors V and/or to communicate the coordinates to the first base station BS1 for such a calculation. As an alternative, the coordinates X1, Y1; X2, Y2 of all abse stations BS1, BS1 can also be stored in each base station. Then each base station is able to determine the directional vector. According to another alternative, it is possible to store, instead of the coordinates, the directional vectors between all abse stations in the central unit RNC and/or the base stations BS1, BS2. However, only the coordinates X1, Y1; X2, Y2 or the directional vectors V of those base stations that are directly adjacent to the respective base station, are stored advantageously in the base stations BS1, BS2, because the signals S1 are transmitted only between these two base stations for the purpose of determining the alignment of their antenna array. In this way each base station has to store only relatively few data.

[0021] The angle gamma between the directional vector V and the reference direction N can be calculated by the known method with the formula for calculating the scalar product of two vectors (a x b = \a\ x \b\ x cos alpha). In an additional step the signals S1, which the second base station BS2 sends to the first base station BS1, are received by the latter. A reception angle beta between the received signals S1 and the alignment AA1 of the antenna array A1 is determined. The determination of the angle of incident of a signal using a directional reception antenna is known to the person skilled in the respective art. In a last step the angle alpha 1 of the alignment AA1 of the antenna array A1 relative to the reference direction N is determined as the difference between the angle gamma of the directional vector V and the reception angle beta.

[0022] The angle alpha 1 of the relative alignmnet AA1 can be determined in its entirety by means of the first base station BS1. To this end, the first radio station BS1 in Figure 3 exhibits a first device U1 for determining the angle gamma of the directional vector V. Furthermore, the first base station BS1 also exhibits a second device U2 for determining the reception angle beta between the signals S1, which are emitted by the second radio station BS2, and the alignment AA1 of the antenna array A1. Moreover, it exhibits a third device U3 for determining the angle alpha 1 of the alignment of the antenna array A1. Furthermore, the first base station BS1 in Figure 3 exhibits a fourth device U4, which serves to transmit the values, determined by the base station BS1, to the central unit RNC from Figure 1. According to Figure 2, the antenna array A2 of the second base station BS2 also exhibits a defined alignment AA2 relative to the reference direction N, which matches an angle alpha 2. In this embodiment all of the base stations BS1, BS2 of the mobile ratio system, depicted in Figure 1, are constructed as shown in Figure 3, so that the central unit RNC receives the angles alpha 1, alpha 2 of the relative alignment of the antenna arrays of all of the base stations BS1, BS2, which are connected to said central unit.

[0023] Another embodiment of the invention makes it possible to implement either the first device U1 of the third device U3 outside the first base station BS1 - for example, in the central unit RNC, depicted in Figure 1. Thus, it is possible for the centralunit RNC to perform the determination of the angle gamma of the directional vector V and to send either to the first base station BS1, which then calculates the angle alpha 1 using the angle gamma, or to use in the central unit RNC in order to calculate the angle alpha 1 to which end it is necessary that the first base station BS1 transmits the value of the angle beta to the central unit RNC. In the former case at least one unit, which corresponds to the first device U1 in Figure 3, has to be disposed in the central unit RNC. In the latter case a unit, which corresponds to the third device U3 from Figure 3, must also be disposed in the central unit RNC.

[0024] The central unit RNC from Figure 1 exhibits, of course, devices for sending and for receiving the said data, exchanged with the first base station BS1.

[0025] At this point Figure 2 will serve to explain in detail the method by which the first base station BS1 determines a relative position of the mobile station MS. To this end, the mobile station MS sends the signals S2 to the first base station BS1, which receives said signals. At this stage the first base station BS1 determines a reception angle ? between these received signals S2 and the alignment AA1 of its antenna array A1. Finally the relative position of the mobile station MS is determined as the difference between the angle alphaa 1 of the alignment AA1 of the antenna array A1 of the fist base station BS1 relative to the reference direction N and the reception angle ? of the signals S2 of the mobile station MS, because in the example, depicted in Figure 2, the sign of the angle alpha 1 is positive, and the sign of the angle ? is negative, the product of forming the difference is an addition of the amounts of the angles alpha 1 and ?.

[0026] The calculation of the relative position of the mobile station MS by forming the said difference may be carried out by either the first base station BS1 or by the central unit RNC. In the former case it is advantageous for the first radio station to communicate then the determined relative position of the mobile station MS to the mobile radio network - for example, to the central unit RNC. In the latter case the first base station BS1 has to transmit its determined reception angle ? beforehand to the central unit RNC.

Patent Claims

1. Method for determining an angle (alpha 1) of the relative alignment (AA1) of an antenna array (A1) of a first radio station (BS1), which exhibits at least two antennas, relative to a reference direction (N), in which method

- an angle (gamma) of a directional vector (V) between the first radio station (BS1) and a second radio station (BS2) is determined on the basis of the reference direction (N),

- signals (S1) are transmitted from the second radio station (BS2) to the first radio station (BS1),

- the signals (S1) are received by the antenna array (A1) of the first radio station (BS1),

- a reception angle (beta) between the received signals (S1) and the alignment (AA1) of the antenna array (A1) is determined,

- and the angle (alpha 1) of the alignment (AA1) of the antenna array (A1) relative to the reference direction(N) is determined as the difference between the angle (gamma) of the directional vector (V) and the reception angle (beta).

2. Method, as claimed in claim 1, wherein

the directional vector (V) is determined from the geographical positions (x1, y1; x2, y2) of both radio stations (BS1, BS2).

3. Method, as claimed in claim 2, wherein

the geographical positions of the radio stations are determined with the aid of a radio-assisted positioning system.

4. Method, as claimed in any one of the preceding claims, wherein the angle (alpha 1) of the alignment (AA1) of the antenna array (A1) is determined in the first radio station (BS1) and then transmitted to a central unit (RNC), which is connected to several radio stations (BS1, BS2).

5. Method, as claimed in any one of the claims 1 to 3, wherein

- the reception angle (beta) between the received signals (S1) and the alignment (AA1) of the antenna array (A1) is determined by the first radio station (BS1) and transmitted to a central unit (RNC), which is connected to several radio stations (BS1, BS2),

- and the angle (gamma) of the directional vector (V) between the first radio station (BS1) and the second radio station (BS2) and/or the difference between the angle (gamma) of the directional vector (V) and the reception angle (beta) is determined by the central unit (RNC).

6. Method, as claimed in any one of the preceding claims, for an additional determination of the relative position of a third radio station (MS), wherein

- the signals (S2), which are emitted from the third radio station (MS), are received by the first radio station (BS1),

- a reception angle (?) between these received signals (S2) and the alignment (AA1) of the antenna array (A1) of the first radio station (BS1) is determined,

- and the relative position of the third radio staion (MS) is determined as the difference between the angle (alpha 1) of the alignment (AA1) of the antenna array (A1) of the fist radio station relative to the reference direction (N) and the reception angle (?) of the singals (S2) of the third radio station (MS).

7. Method, as claimed in claim 7, wherein

- the first and the second radio station (BS1, BS2) are stationary stations; and the third radio station (MS) is a mobile station.

8. Method, as claimed in any one of the preceding claims, wherein the first and the second radio station (BS1, BS2) are base stations in a mobile radio system.

9. Radio system exhibitng at least a fist and a second radio station (BS1, BS2),

- whose first radio station (BS1) exhibits an antenna array (A1),

- with a device (U1) for determining an angle (gamma) of a directional vector (V) between the first radio station (BS1) and the second radio station (BS2), relative to a reference direction (N),

- with a device (U2) for determining a reception angle (beta) between the signals (S1), which are emitted by the second radio station (BS2) and received by the first radio station (BS1), and the alignment (AA1) of the antenna array (A1) of the first radio station (BS1),

- and with a device (U3) for determining the angle (alpha 1) of the alignment (AA1) of the antenna array (A1) of the first radio station (BS1) relative to the reference direction (N) as the difference between the angle (gamma) of the directional vector (V) and the reception angle (?).

10. Radio station (BS1)

- with an antenna array (A1),