Abstract:
A communication system and associated method are provided, wherein a quality of service is detected in the communication system, coordination reorganization is performed in order to reorganize coordination functionalities for available stations in the communication system, the previous two steps are repeated for various coordination organizations in the communication system, the various qualities of service detected in the various coordination organizations are analyzed, and a coordination organization is selected on the basis of this analysis, whereupon communication is affected with an external communication system which uses the same transmission medium as the communication system.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a communication system and associated method for improving its quality of service, and particularly to a communication system and an associated method when there is a jointly used transmission medium. 
   Such a communication system and associated method are disclosed in WO 99/11081 A, where a number of subscriber stations in a mobile radio network are provided and can each perform either a master function or a slave function. The functions are distributed over the subscriber stations by evaluating quality-of-service measurements in the mobile radio system. 
   A significant escalation in, by way of example, cordless communication systems means that, in the future, the case will frequently arise that two or more independent communication systems use the same transmission medium, such as frequency bands. This can result in interference or even in one or more of these communication systems failing. 
   When using, by way of example, two communication systems which operate on the basis of the same transmission method or transmission format (e.g., DECT), the standards stipulate methods for avoiding such interference. These conventional methods are known, by way of example, by the term dynamic channel allocation. This allows interference and collisions between independent communication systems to be prevented to a certain degree. 
   Particularly when using independent communication systems which operate on the basis of different transmission methods and use a common transmission medium, such as Bluetooth, HomeRF, Powerline Communications (PLC), etc., interference which is sometimes considerable arises which can even result in one type of communication system failing. With a jointly used transmission medium, such as the ISM frequency band (Industrial, Scientific, Medical), in which a large number of communication systems can operate up to a predetermined transmission level, there therefore can be a high level of interference or incomplete utilization of the resources of the jointly used transmission medium. To be more precise, by way of example, a communication system can no longer work, or can work only inadequately, in a jointly used transmission medium in which, by way of example, microwaves, radio remote controls, babyphones and the like are also operating. 
   The present invention is, therefore, directed toward a communication system and associated method for improving its quality of service which are simple and expensive to achieve. 
   SUMMARY OF THE INVENTION 
   Particularly, the use of coordination changeover switches in a base station and in at east some further stations in the communication system for changing over various coordination functionalities, a quality-of-service detection apparatus for detecting a quality of service in the communication system and an analysis apparatus for analyzing the quality of service, with the coordination changeover switches being controlled on the basis of the analysis performed, allows an optimum quality of service to be achieved in the communication system and allows interference signals to be evaded. 
   Preferably, the quality-of-service detection apparatus or the analysis apparatus can detect or analyze a transmission quality for transmission resources split in the space domain, in the time domain and/or in the domain of frequency or code. This allows not just optimum spatial coverage to be provided in the communication system, but also optimum adjustment in line with any interference signals arising in predetermined time or frequency domains. 
   In addition, at least some of the stations can have an external transmission interface for implementing data transmission with external communication systems, which allows consultation to be instigated between different communication systems for the purpose of improving a respective quality of service. 
   Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Invention and the Figures. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
       FIG. 1  shows a simplified illustration of a communication network having two communication systems with no improvement of a quality of service. 
       FIG. 2  shows a simplified illustration of a communication network having two communication systems following improvement of a quality of service in line with a first exemplary embodiment. 
       FIG. 3  shows a simplified illustration of a communication network having two communication systems following improvement of a quality of service in line with a second exemplary embodiment. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a simplified illustration of a communication network having two communication systems KS 1  and KS 2  which use a common transmission medium. Examples of such communication systems are, by way of example, systems such as Bluetooth, HomeRF, IEEE 802.11, etc. However, the present invention is not limited thereto, but instead similarly covers wired communication systems, such as line-connected multicarrier systems known as HomePNA, PLC, etc. In all these systems, a common transmission medium can be used by a large number of independent communication systems. 
   In line with  FIG. 1 , the communication system KS 1  has a base station B 1  with a point/multipoint connection to further stations T 11  to T 15 . In a cordless application, such further stations are the mobile subscriber terminals, for example. A dashed line in  FIG. 1  denotes a maximum communication range for a respective communication system. In line with  FIG. 1 , a further communication system KS 2  with a shorter range is situated within the range of the communication system KS 1 . The communication system KS 2 , in turn, has a base station B 2  and a large number of further stations or mobile subscriber terminals T 21  to T 24 . 
   In the case of the communication network having communication systems with no improvement of a quality of service, as shown in  FIG. 1 , a situation first arises in which the base station B 1  in the communication system KS 1  cannot hear or detect the communication system KS 2  due to the latter&#39;s short range. Conversely, however, by way of example, the base station B 2  or the master in the communication system KS 2  can identify the communication system KS 1  and can detect that its quality of service is impaired due to interference. In the extreme case, this situation results in the communication system KS 2  being affected by interference from the communication system KS 1  such that it is sometimes not capable of operation. In addition, in the situation shown in  FIG. 1  with no improvement of a quality of service, the case arises that a station T 24  is situated outside the range of the communication system KS 2  and is thus not included, or is included only with a very poor quality of service. 
   A quality of service (QoS) is understood, in line with the present invention, to mean essentially a transmission quality for communication links separated into a time domain, a frequency domain, a code domain, a space domain, etc., for a jointly used transmission medium. The transmission quality can be determined as a bit error rate, for example. To be more precise, a quality of service in a time domain refers to a transmission quality being provided over a maximum period. If there is, by way of example, an interference signal whose effect is limited over time, then a quality of service in the time domain can be improved by virtue of the time domains which are not affected by interference being used optimally for transmission. In the same way, a quality of service in the frequency domain relates to a transmission quality in predetermined bandwidth channels or carriers in a jointly used transmission medium. A quality of service in the frequency domain can be improved, by way of example, by virtue of the frequency domain of the interference signal being cut out and only carriers or channels which are not affected by interference being used for transmission. Finally, a quality of service in a space domain relates to a transmission quality in a space domain of the whole communication system, with a maximum coverage or an optimum transmission quality being attempted for all available stations. In addition, a quality of service can be improved by virtue of a communication system having a way of communicating with external communication systems, and this instigating consultation for the purpose of improving a quality of service in a whole communication network. 
   To improve a quality of service in the space domain, the base station and at least some of the further stations T 21  to T 24  have a coordination changeover switch for changing over a respective coordination functionality between participating stations. By way of example, such a coordination functionality for improving a quality of service in the space domain can be a point/point or point/multipoint connection in the respective stations of the communication system. To be more precise, at least some of the stations in the communication system KS 2  thus have the ability to operate either as a “master” or as a “slave”. In line with  FIG. 1 , the base station B 2  first provides a point/multipoint connection or a master in the communication system KS 2 , while the further stations T 21  to T 24  have point/point connections. 
   In addition, the communication system KS 2  has a quality-of-service detection apparatus which is preferably located directly in the stations and, by virtue of interchange with all stations, for example, ascertains a respective quality of service for a particular coordination functionality for a whole communication system KS 2 . In the situation shown in  FIG. 1 , such a quality-of-service detection apparatus will detect an impaired quality of service (in the space domain), since the station T 24  is situated outside the range of the communication system KS 2 . In addition, there is a high level of interference due to the higher-level communication system KS 1 . 
   To improve a quality of service at least in the communication system KS 2 , coordination reorganization is therefore performed systematically or randomly for the communication system KS 2 . To be more precise, each station T 21  to T 24  is switched, for example successively, to a point/multipoint-connection coordination functionality or a “master mode” and a respective quality of service is detected in the communication system KS 2 . Following repeated performance of this coordination reorganization and associated quality-of-service detection, the detected qualities of service are finally analyzed by an analysis apparatus and, on the basis of the analysis result, the coordination organization which allows the best quality of service or best spatial coverage is selected. 
   In line with  FIG. 2 , such an improvement in the quality of service (e.g., in the space domain), is obtained as a result of a coordination organization in which one station T 21  now operates as a point/multipoint connection or master and the other stations T 22  to T 24  and the earlier base station B 2  work as point/point connections or slaves. In this way, it is possible to shift the range of the communication system KS 2  such that it is now also possible to reach the station T 24 , which gives maximum spatial coverage for all the stations in the communication system KS 2 . In addition, moving the master from the base station B 2  to the station T 21  provides contact with the base station B 1  in the communication system KS 1 , however, which now provides this communication system with knowledge of the existence of a further communication system for the first time. Although one quality of service (transmission quality) in the communication system KS  2  is impaired due to increased interference by the communication system KS  1 , the advantage of such an active strategy is that the communication system KS 1 , provided that it is an intelligent system, now implements an appropriate evasion strategy and, by way of example, reduces a transmission level or the range of the communication system to a minimum. This allows a quality of service or a transmission quality to be significantly improved in a whole communication network KS 1  and KS 2 , since a quality of service in the communication system KS 2  has now been significantly improved without impairing the quality of service in the communication system KS 1 . 
   In line with  FIG. 3 , following improvement of a quality of service, a second exemplary embodiment allows not only the spatial coordination reorganization implemented in  FIG. 2  but also setup of external communication between the communication system KS 1  and the communication system KS 2 . To implement such data transmission with external communication systems, each station additionally has an external transmission interface besides an internal transmission interface for implementing data transmission within the communication system, which allows consultation to take place between the two communication systems. In the course of such consultation, the jointly used transmission medium now can be split in the space domain, in the time domain, in the code domain and/or in the frequency domain such that a respective optimum quality of service or transmission quality is obtained for the communication systems KS 1  and KS 2 . In this context, it is fundamentally true that a communication system is more robust the more free parameters there are for implementing an evasion strategy. 
   If the communication system KS 1  is a “frequency hopper”, for example, then quality of service in the time domain can be improved, by way of example, by virtue of analysis of the temporally recurrent frequency jumps in the communication system KS 1  being succeeded by the communication system KS 2  following the system KS 1  with a time delay, which prevents collision at all times. In this case, it is possible to use both the same frequency domain (bandwidths or carriers) and identical space domains. 
   In the same way, such a communication system and the associated method for improving its quality of service also can react to problematic sources of interference, such as microwaves, babyphones, radio remote controls and the like. The systematic detection and analysis of the sources of interference or of the qualities of service obtained allow the inventive communication system and the associated method to be used to develop an evasion strategy such that an available spectrum in a jointly used transmission medium is utilized in optimum fashion, and both more robust and more reliable communication systems are produced. 
   The invention has been described above with reference to a cordless communication system. It is not limited thereto, however, and instead comprises all other communication systems, such as line-connected multicarrier systems, which use a jointly used transmission medium. 
   Indeed, although the present invention has been described with reference to specific embodiments, those of skill in the art will recognize that changes may be made thereto without departing from the spirit and scope of the present invention as set forth in the hereafter appended claims.