Abstract:
The present invention relates to a fixed transmitting station of a wireless telecommunication system comprising:  
     antenna means ( 104, 106, 108 )  
     measurement means ( 110, 112 ) for electromagnetic field measurements of an electromagnetic environment of the antenna means,  
     means ( 112, 118, 116, 120, 122 ) for transmitting of data being indicative of a measurement result to a central control unit ( 124 ).

Description:
[0001]    The invention is based on a priority application EP 02 360 378.0 which is hereby incorporated by reference.  
         FIELD OF THE INVENTION  
         [0002]    The present invention relates to the field of wireless telecommunication systems, and more particularly without limitation to the measurement of electromagnetic fields around fixed transmitting stations, such as base station antennas.  
         BACKGROUND AND PRIOR ART  
         [0003]    According to national and international regulations (e.g. EC recommendation 1999/519/EC and RTTE Directive 1999/5/EC), when a base station (BTS) is put into service, it is mandatory to comply with the essential safety requirements, in particular those related to human exposure to RF emissions. In-situ compliance assessment depends on the EM environment (EME). It is impacted by reflection and diffraction from nearby objects and by emissions from other sources (e.g. broadcast, FM . . . ) or from other mobile networks (GSM or UMTS). This problem is particularly important in a context of site sharing.  
           [0004]    To date, operators or regulatory agencies have to make in-situ measurements to verify a posteriori that the EM environment has not changed since the base station has been put into service.  
           [0005]    Usually a measurement equipment consisting of an electromagnetic field probe and a measurement device (e.g. a spectrum analyser or a voltmeter) which is controlled by a laptop is used for performing the electromagnetic field survey. By means of such a measurement, an accurate verification can be performed that the applicable electromagnetic exposure limits, which have been issued by the competent authority have been met. To date, exposure limits for the general public are defined by the European recommendation 1999/519/EC.  
           [0006]    The methods for compliance assessment are defined by CENELEC (European Committee for electrotechnical standardisation, documents from TC 106X WG1) under the mandate M305 of the European Commission. Compliance assessment of a base station is performed according to the standards EN50383 to EN50385, when the equipment is put on the market. Compliance assessment when the base station is put into service is performed according to the draft European standards prEN50400 and prEN50401. European standards for market enforcement and in-situ measurements are currently being drafted. A large number of protocols have been established on a national basis (for example in France by Agence Nationale des fréquences ‘in situ measurement protocol’, edition 2001) or on an international basis (for example CEPT 02 04 “measuring non-ionizing radiation (9 kHz-300 GHz)” from the Electronic Communications Committee (ECC) within the European Conference of Postal and Telecommunications Administrations (CEPT)). In particular, those standards apply when a base station of a cellular telecommunication system is installed.  
           [0007]    However, these norms also have to be met during operation of the base station, especially when the electromagnetic environment has changed. For this purpose, electromagnetic field exposure surveys are performed by the operators or the regulatory agencies. The disadvantage of this procedure is that monitoring of EME changes with a posteriori in-situ measurements requires a lot of manpower (cf. C. Olivier, L. Martens, “Measuring techniques for the exposure assessment around base stations for mobile communications”, Proceedings of the 9th URSI Forum 2001, 13 Dec. 2001, Louvain-la-Neuve, Belgium, pp. 5. C.; Olivier, L. Martens, “A practical method for compliance testing of base stations for mobile communications with exposure limits”, Proceedings of the 2001 IEEE AP-S International Symposium and USNC/URSI National Radio Science Meeting, Vol. 2, 8-13 Jul. 2001, Boston, Mass., USA, pp. 64-67; C. Olivier, L. Martens, “Measurements of exposure to electromagnetic radiation around GSM base stations in Belgium: a base for a practical measuring procedure”, Abstract book of the BEMS Twenty-Third Annual Meeting in cooperation with the European Bioelectromagnetics Association, 10-14 Jun. 2001, St. Paul, Minn., USA, pp. 102-104; W. Joseph, L. Martens, “Calibration of field probes and study of the disturbance on the evaluation of electromagnetic fields”, Proceedings of the 9th URSI Forum 2001, 13 Dec. 2001, Louvain-la-Neuve, Belgium, pp. 48.).  
           [0008]    The present invention therefore aims to provide an improved method of monitoring a fixed transmitting station.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention provides a method of monitoring implemented on a fixed transmitting station of a wireless telecommunication system. For example, the fixed transmitting station can be a base station (BTS) of a GSM cellular mobile telecommunication system or it can be a node-B of a UMTS system. Such a fixed transmitting station has an antenna for sending and receiving of electromagnetic signals. The in-situ compliance assessment in the vicinity of the antenna depends on electromagnetic fields emitted by the antennas itself as well as the electromagnetic environment of the antenna. The electromagnetic environment may vary over time when additional systems are installed which emit electromagnetic fields.  
           [0010]    The present invention is particularly advantageous in that any relevant change in the electromagnetic environment is detected automatically without manual interaction and is reported to a central control unit. This enables an operator to ensure at all times that the applicable regulations are met.  
           [0011]    In accordance with a preferred embodiment of the invention one or more electromagnetic field probes are fixed to the antenna for performing the electromagnetic field measurements. For example, a measurement probe can be mounted on top of the antenna and/or on the rear panel of the antenna and/or on the shelter of an outdoor base station and/or at any place in the vicinity of the main lobe of the emitting antenna.  
           [0012]    In accordance with a further preferred embodiment of the invention the electromagnetic field probes are coupled to a measurement device for receiving of the measurement signals from the probes. The measurement device provides measurement data which is transmitted to a central control unit and processed. On the basis of this measurement data the fixed transmitting station can be centrally monitored.  
           [0013]    In accordance with further preferred embodiment of the invention the measurement data provided by the measurement device is imputed into the base station of the fixed transmitting station via an appropriate interface. From there the measurement data are transmitted to an operations and maintenance centre. In the operations and maintenance centre the measurement data is processed and monitored. Alternatively some or all of the processing is done on the level of the base station and only the data processing results are transmitted to the operations and maintenance centre. The same applies analogously to a UMTS-type network where a node-B is used instead of a base station.  
           [0014]    In accordance with a further preferred embodiment of the invention the electromagnetic field measurements are not only used for the purposes of monitoring of the fixed transmitting station but also for controlling of radio network parameters of the wireless communication system. For example when a drift of the EME parameters is detected one or more of the radio link parameters are adapted correspondingly in order to ensure that despite the drift of EME parameters all of the applicable regulations are still met. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    In the following preferred embodiments of the invention will be described in greater detail by making reference to the drawings in which:  
         [0016]    [0016]FIG. 1 shows a fixed transmitting station being coupled to an operations and maintenance centre,  
         [0017]    [0017]FIG. 2 shows an alternative embodiment of the fixed transmitting station of FIG. 2,  
         [0018]    [0018]FIG. 3 is a flow chart being illustrative of a method of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0019]    [0019]FIG. 1 shows a fixed transmitting station  100  having an antenna mast carrying antennas  104 ,  106  and  108 . Probes  110  are mounted atop antennas  104 ,  106  and  108  and/or on the rear panels of antennas  104 ,  106  and  108  and/or near to or on the shelter of the base station  120  and/or at any place in the vicinity of the main lobe of antennas  104 ,  106  and  108 . The probes  110  are coupled to a measurement device  112  by means of cables  114 . In one embodiment, the probe  110 , cables  114  and the measurement device  112  are integrated in a measurement equipment.  
         [0020]    Measurement device  112  is coupled to interface unit  116  by means of cable  118 . Interface unit  116  provides an interface between the measurement device  112  and base station  120 . Alternatively base station  120  has an integrated interface module  122  in order to directly connect the cable  118  to the base station  120 , i.e. to interface module  122  of base station  120 .  
         [0021]    Base station  120  is coupled to operations and maintenance centre  124 . Base station  120  collects a variety of telecommunication parameters, such as the actual telecommunication traffic in the cell which is serviced by fixed transmitting station  100  and provides those parameters to operations and maintenance centre  124 . On the basis of these parameters, radio link parameters of the fixed transmitting station  100  can be adapted by the operations and maintenance centre  124 .  
         [0022]    By means of the probes  110  electromagnetic field measurements are performed for measuring of the electromagnetic environment of the antennas  104 ,  106  and  108 . The corresponding measurement signals which are provided by the probes  110  are transmitted via cables  114  to measurement device  112 . Measurement device  112  transforms the measurement signals provided by the probes  110  into measurement data signals being indicative of the measured field strength. These measurement data are provided either indirectly via interface unit  116  or directly via interface module  122  to the base station  120 .  
         [0023]    In one embodiment, base station  120  forwards the measurement data to operations and maintenance centre  124 . In this instance the data monitoring and processing is performed in the operations and maintenance centre. Alternatively some or all of the processing is performed locally by the base station  120  itself and only the results of the data processing are transmitted to the operations and maintenance centre  124 . The data monitoring and processing functionality which is implemented in the base station  120  and/or in the operations and maintenance centre  124  provides data related to electromagnetic field levels and/or to any drift of EME parameters in the vicinity of the fixed transmitting station  100 . By means of the data processing potential problems are detected. Further appropriate warning and/or alert messages are generated on this basis and monitored, at the level or the operations and maintenance centre  124  and /or at the level of the base station  120 .  
         [0024]    In addition the radio link parameters of the fixed transmitting station  100  can be controlled on the basis of the electromagnetic field measurements. For example, if a drift of the EME parameters is detected the operations and maintenance centre  124  can adapt the radio link parameters of the fixed transmitting station  100  correspondingly in order to ensure that all regulatory norms are met at all times. It is to be noted that the probe  110  and the measurement device  112  can be integrated into antenna  104 ,  106  and  108 .  
         [0025]    [0025]FIG. 2 shows an alternative embodiment of fixed transmitting station  1   00 . Elements of FIG. 2 corresponding to elements of FIG. 1 are designated with the same reference numerals.  
         [0026]    In the embodiment of FIG. 2 the antennas  104 ,  106  and  108  are coupled to base station  120  by means of radio frequency cables  130 ,  131  and  132 , respectively. Radio frequency cable  130  serves for transmitting of radio frequency up-link and down-link signals between antenna  104  and base station  120 . Likewise radio frequency cable  131  serves for transmission of such up-link and down-link signals between antenna  106  and base station  120  and radio frequency cable  132  serves for transmission of such signals between antenna  108  and base station  120 .  
         [0027]    In the example considered here the measurement probes  110  are integrated into the antennas  104 ,  106  and  108 . The radio frequency cables  130 ,  131  and  132  have an additional functionality which is to interconnect the probes  110  to measurement device  112  and to interconnect measurement device  112  to interface module  122  or interface unit  116 . This way a separate cable  118  between the measurement device  112  and interface module  122  or interface unit  116  can be replaced. This has the advantage of minimizing site commissioning and therefore reduces the cost and time required to set up a site. Additional electronics can be provided at both ends of radio frequency cables  130 ,  131  and  132  for coupling and de-coupling with radio frequency signals.  
         [0028]    Alternatively one of the radio frequency cables  131 ,  131  or  132  is used to provide a power supply to measurement device  112  in addition to the transmission of the radio frequency up-link and down-link signals between the antennas and the base station  120 . In this instance probes  110  are coupled to measurement device  112  by separate cables. The transmission of the measurement data from the measurement device  112  to the interface module  122  is performed by means of a wireless link  119  between the measurement device  112  and base station  120 .  
         [0029]    It is to be noted that in all of the embodiments considered above the measurement probes  110  can be either mounted on or integrated in the antenna means and/or mounted on/or near the base station shelter and/or installed at any place in the vicinity of the main lobe of antennas  104 ,  106  and  108 .  
         [0030]    [0030]FIG. 3 shows a corresponding flow chart. In step  200  ongoing electromagnetic field measurements are performed in order to monitor electromagnetic environment of the antenna of a fixed transmitting station. The corresponding measurement signals are converted in step  202  into measurement data being representative of the measured electromagnetic field parameters. As an option, data processing is performed in step  202  in order to pre-process the data before it is reported to an operations and maintenance centre in step  204 . In step  206  an assessment is made by the operations and maintenance centre whether the measured electromagnetic field parameters are within a desired range. If this is the case no further action needs to be taken and further measurement results are evaluated at periodic intervals by repeating steps  200  to  206 .  
         [0031]    If the electromagnetic field parameters are not within the desired range, an alert signal is generated and processed. In step  207  the alert is processed. Depending on the alert level, the radio network parameters may be adapted or other actions, for example local signalling or more accurate in-situ measurements, can be performed correspondingly in step  208 .  
         [0032]    The integration of the electromagnetic field measurements into the fixed transmitting station is advantageous both for setting up the fixed transmitting station and for its operation. When the fixed transmitting station is installed the electromagnetic environment is assessed locally. Then, during operation this procedure enables real-time monitoring of the electromagnetic environment and any drifts or changes which may occur. This ongoing site monitoring is especially useful in the case of site sharing.  
         [0033]    This feature is especially useful when an additional telecommunication system is set up and site-sharing is used. For example if the fixed transmitting station belongs to a GSM system and an additional node-B of a UMTS system is installed next to the existing base station this may abruptly change the electromagnetic environment which is immediately reported back to the operations and maintenance centre. In response any required adaptations can be performed.  
         [0034]    List of Reference Numerals  
         [0035]    [0035] 100  fixed transmitting station  
         [0036]    [0036] 102  antenna mast  
         [0037]    [0037] 104  antenna  
         [0038]    [0038] 106  antenna  
         [0039]    [0039] 108  antenna  
         [0040]    [0040] 110  probe  
         [0041]    [0041] 112  measurement device  
         [0042]    [0042] 114  cable  
         [0043]    [0043] 115  measurement equipment  
         [0044]    [0044] 116  interface unit  
         [0045]    [0045] 118  cable  
         [0046]    [0046] 119  wireless link  
         [0047]    [0047] 120  base station  
         [0048]    [0048] 122  interface module  
         [0049]    [0049] 124  operations and maintenance centre  
         [0050]    [0050] 130  radio frequency cable  
         [0051]    [0051] 131  radio frequency cable  
         [0052]    [0052] 132  radio frequency cable