Abstract:
The present invention relates to a method of operating a communications network, wherein resources required for transmitting data within said communications network, in particular for transmitting data from a subscriber station to a first base station, are granted depending on a request for said resources. At least one further base station is provided with scheduling information related to said request for said resources.

Description:
[0001]     The invention is based on a priority application EP 04 292 715.2 which is hereby incorporated by reference.  
       TECHNICAL FIELD  
       [0002]     The present invention relates to a method of operating a communications network, wherein resources required for transmitting data within said communications network, in particular for transmitting data from a subscriber station to a first base station, are granted depending on a request for said resources.  
         [0003]     The present invention further relates to a base station for a communications network, wherein resources required for transmitting data within said communications network, in particular for transmitting data from a subscriber station to said base station are granted depending on a request for said resources.  
       BACKGROUND OF THE INVENTION  
       [0004]     Such systems are known from prior art and can inter alia be used to form a so-called multi-hop network architecture which offers the possibility to exchange data between neighbouring radio cells each of which is associated to a base station of the communications network. Since said exchange can be performed by means of a radio frequency (RF) interface provided within said base stations, a backbone connecting the base stations e.g. with optical fiber means or the like is not required.  
         [0005]     The major disadvantage of such a wireless multi-hop network architecture based on contemporary systems consists in comparatively large delays which usually amount to a multiple of respective transmit frame units, depending on the system and communications protocol used.  
         [0006]     Said delay may i.e. reach tens of milliseconds and thus has a service-degrading influence especially on services such as voice over IP (VoIP) and the like.  
       SUMMARY OF THE INVENTION  
       [0007]     Therefore, it is an object of the present invention to provide an improved method of operating a communications network and an improved base station to achieve reduced delays in particular when being operated in multi-hop configurations as compared to prior art systems.  
         [0008]     Regarding the method of operating a communications network, wherein resources required for transmitting data within said communications network, in particular for transmitting data from a subscriber station to a first base station, are granted depending on a request for said resources, said object is achieved by providing at least one further base station with scheduling information related to said request for said resources.  
         [0009]     Resources in the above sense may e.g. be free transmission time frames/time slots, bandwidth, transmission channels and the like.  
         [0010]     By using the above mentioned inventive method, it is possible to timely prepare the further base station for a future data transmission. The steps which are necessary in said further base station to prepare a future data transmission like scheduling transmission time frames and the like can thus be performed in parallel to the processing of the request issued by the subscriber station within the first base station, i.e. even before the subscriber station itself performs a data transmission to the first base station.  
         [0011]     Therefore, for a subsequent data transmission from the first base station to the further base station in accordance with the multi-hop principle, there are no further delays due to a further grant getting process because at the moment the first base stations initiates the data transmission to the further base station, said further base station is already prepared for said data transmission because it has been able to reserve the corresponding resources in advance to the data transmission.  
         [0012]     In difference to the prior art systems, individual delays corresponding to processing requests within a base station do not accumulate when using the inventive method. The delays accumulate in conventional systems due to the fact that resources for transmitting data are scheduled independently for or within each base station, respectively.  
         [0013]     Those partly unavoidable delays for processing the requests and for a subsequent reserving and granting of resources are cascaded in a sophisticated way by forwarding the scheduling information to the further base station according to the present invention.  
         [0014]     Recursive forwarding is also possible according to the present invention, i.e. upon receiving scheduling information from the first base station, the further base station may, in turn, forward said scheduling information to a base station which is designated as the destination for the next hop within the multi-hop network architecture.  
         [0015]     According to an advantageous embodiment of the present invention said request is provided prior to processing said request in said first base station. This variant provides the fastest possible forwarding of the request to further base stations or other network elements.  
         [0016]     According to a further advantageous embodiment of the present invention, said scheduling information is provided during or after processing said request in said first base station which enables to provide the further base station(s) with more exact scheduling information since information contained within the request of the subscriber station has been evaluated by the first base station at that stage.  
         [0017]     According to another advantageous embodiment of the present invention said scheduling information comprises timing information denoting a specific time and/or time interval at/during which resources of said further base station are to be reserved, in particular for a data transmission originating from said first base station.  
         [0018]     The timing information can be used for various purposes within the further base station(s). Firstly, the timing information determines for the further base station(s) when to provide the resources required.  
         [0019]     It is possible to use an absolute time format for said timing information such as a time of day or the like. In this case, both base stations must have synchronized system clocks.  
         [0020]     A further possibility to represent timing information comprises denoting an open time interval starting at a specific time of day by said timing information which also requires synchronized system clocks.  
         [0021]     It is also possible to use the timing information as a differential time value which defines a time interval after which—e.g. upon reception of the timing information within the further base station—the required resources are to be provided.  
         [0022]     Secondly, the timing information enables to perform a sophisticated, implicit synchronization of a plurality of base stations without overhead.  
         [0023]     According to a further advantageous embodiment of the present invention said scheduling information comprises information on the amount of data to be transmitted which enables an even more precise synchronisation of a multi-hop data transmission.  
         [0024]     According to a further very advantageous embodiment of the present invention said scheduling information is optimised based on measured delays. Such measured delays may e.g. comprise the delay between receiving scheduling information or timing information, respectively, and the time of arrival of the transmitted data indicated by the previously received scheduling information. By evaluating said delay, future scheduling information may be corrected depending on the previously measured delay to improve reliability of the inventive method.  
         [0025]     A further very advantageous embodiment of the present invention is characterized by using feedback information relating to said scheduling information, wherein said feedback information is issued by said further base station and/or by any other network element of said communications network involved in a data transmission.  
         [0026]     Said feedback information may e.g. comprise a measured delay obtained by the further base station as described above. By transmitting said feedback information to the first base station, it is possible to perform a closed-loop control of the multi-hop forwarding process.  
         [0027]     According to the present invention, it is also possible to transmit feedback information from further network elements such as a receiving subscriber station and the like to the first base station.  
         [0028]     Said transmission of feedback information can also be performed depending on the data transmission. It is, for instance, possible to transmit feedback information only upon errors.  
         [0029]     According to a further advantageous embodiment of the present invention a controller for distributing said scheduling information among said base stations and/or other network elements involved in a data transmission is provided.  
         [0030]     The controller ensures a proper distribution of the scheduling information and enables to bridge a base station of the multi-hop network architecture which is not capable of performing the inventive method.  
         [0031]     Regarding the base station for a communications network, wherein resources required for transmitting data within said communications network, in particular for transmitting data from a subscriber station to said base station, are granted depending on a request for said resources, the object of the present invention is achieved by providing means for providing at least one further base station with scheduling information related to said request for said resources.  
         [0032]     According to an advantageous embodiment of the present invention said means for providing at least one further base station with scheduling information comprise a subscriber station.  
         [0033]     This is particularly advantageous for use with communication protocols which e.g. do not support a direct communication of two base stations via their radio interfaces. In this case, any data which is to be transmitted from a first base station to a second base station is forwarded from the first base station to a subscriber station reserved for this purpose which, in turn, transmits the data so received in a classic uplink manner to the second base station. This way it is possible to use conventional base stations for implementing the present invention without changing the RF/wireless interface of the base stations to enable an inter-base station communication in an uplink fashion.  
         [0034]     The scheduling information may also solely consist of the request for said resources.  
         [0035]     Generally, the method according to the present invention is independent of the specific mechanism that is used for the procedure of requesting resources required for data transmissions and for granting these resources.  
         [0036]     For instance, the method according to the present invention can be performed together with the following granting mechanisms known from prior art:  
         [0037]     UGS (Unsolicited Granting Service), in which a regular pattern of grants is delivered to a subscriber station without an individual request of the subscriber station. The UGS is usually employed for fixed bit rate data transmission and/or for connection oriented services like voice services.  
         [0038]     RTP (Real Time Polling), wherein a subscriber station is polled frequently and periodically with opportunities to request for grants in a collision free manner. RTP is also well suited for voice services such as voice over IP (VoIP).  
         [0039]     NRTP (non-RTP), which resembles RTP but which has a reduced polling rate and a less regular polling pattern. NRTP granting mechanisms optionally provide a support of a minimum bandwidth.  
         [0040]     Contention based granting, in which all subscribers compete for access.  
         [0041]     The inventive method provides a systematic approach for minimising the delay of multi-hop data transmission and jitter by evaluating feedback information e.g. on an on-demand basis.  
         [0042]     Another obvious advantage arising from the application of the inventive method is the minimisation of data and/or packet storage space that has to be provided in the inventive base stations since forwarding delays are significantly reduced by the inventive recursive forwarding of scheduling information.  
         [0043]     The inventive method can also be operated so as to focus the possible optimisations to one of the aforedescribed issues of delay minimisation, jitter minimisation and minimisation of data and/or packet storage space.  
         [0044]     A further advantage of the present invention is the independence of the inventive method of any underlying standards, e.g. concerning the transmission of data between a subscriber station and a base station and the like.  
         [0045]     Though losing some of the benefits of the present invention, an inventive base station comprises full interoperability with prior art base stations. Furthermore, the inventive method is transparent to subscriber stations and does therefore not require any changes of subscriber station hardware or software.  
         [0046]     Although the present invention is not limited to a special network communications system or standard, it is well suited for being implemented within networks operating according to IEEE 802.16 family specifications. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0047]     Further advantages and features of the present invention are described in the following detailed description with reference to the drawings in which  
         [0048]      FIG. 1  shows a typical scenario employing a first embodiment of the present invention, and  
         [0049]      FIG. 2  shows a message flow according to the embodiment of the present invention referred to in  FIG. 1 .  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0050]     The communications network  100  depicted in  FIG. 1  comprises a plurality of base stations  10 ,  20 ,  30 ,  40  each of which defines a radio cell  12 ,  22 ,  32  in which wireless data transmission is possible between subscriber stations  13  of the respective radio cell  12  and the corresponding base station  10 .  
         [0051]     The base stations  10 ,  20 ,  30  and  40  are not connected by a backbone e.g. in form of a cable connection or the like which necessitates employing a wireless data transmission in order to exchange data between different base stations  10 ,  20 ,  30 ,  40 .  
         [0052]     The wireless data transmission of e.g. the first base station  10  to the further base station  20  is realised by means of an RF connection symbolized by the triangle  11 ′. Said RF connection  11 ′ is maintained from a subscriber station  11  which is assigned to the first base station  10  and connected by the link  10 ′.  
         [0053]     The advantage of using the subscriber station  11  for the mentioned data transmission of the first base station  10  to the further base station  20  is based on the compatibility of this solution with existing network communications standards which do not provide for a direct communication of two base stations  10 ,  20  in an uplink fashion. However, a typical uplink connection scenario as performed by the subscriber station  11  and the further base station  20  does not cause any problem.  
         [0054]     In the same way, wireless data transmissions are performed from the base station  20  to the base station  30  and from the base station  30  to the base station  40 . For this purpose, each of the further base stations  20 ,  30  is assigned a special subscriber station  21 ,  31  linked to the respective base stations  20 ,  30  by the links  20 ′,  30 ′ as depicted in  FIG. 1 .  
         [0055]     To perform a multi-hop data transmission from the subscriber station  13  to the destination network element  50 , the inventive method of recursively requesting resources for data transmission from a neighbour base station is performed, which is described below with reference to  FIG. 2 , in which the vertical lines denoted with reference numerals  13 ,  10 ,  20 ,  30 ,  40  represent the respective network element of the communications network  100  of  FIG. 1 , i.e. the base stations  10 ,  20 ,  30 ,  40  and the subscriber station  13  situated within the radio cell  12  of base station  20 .  
         [0056]     In order to initiate the multi-hop data transmission, the subscriber station  13  sends a request  200  ( FIG. 2 ) for resources such as transmission time frames or time slots to the first base station  10 .  
         [0057]     Upon receiving said request  200 , the base station  10  processes the request within step  300  of  FIG. 2 . As a result of said processing, transmission time frames or time slots or further resources required for the desired data transmission of subscriber station  13  are reserved by the base station  10  and a corresponding timing information is created.  
         [0058]     It is possible to use an absolute time format for said timing information such as a time of day or the like. In this case, any base station included in the multi-hop path is required to have its system clock synchronized with the other base stations.  
         [0059]     A further possibility to represent timing information comprises denoting an open time interval starting at a specific time of day by said timing information which also requires synchronized system clocks.  
         [0060]     It is also possible to use the timing information as a differential time value which defines a time interval after which—e.g. upon reception of the timing information within the further base station  20 —the required resources are to be provided.  
         [0061]     After the step of processing  300 , the base station  10  provides the further base station  20 , which is the next destination of the multi-hop data transmission, with scheduling information  210  which is related to said request  200  of the subscriber station  13 .  
         [0062]     The scheduling information  210  comprises information on the request  200  and the timing information previously created in the first base station  10  upon the request  200  and is used within the further base station  20  to reserve corresponding resources for the expected time of arrival of data originating from the subscriber station  13  which is forwarded by the first base station  10  to the further base station  20  according to said timing information.  
         [0063]     Subsequent requests  220 ,  230  ( FIG. 2 ) of the aforedescribed type are subsequently issued from the base station  20  to the base station  30 , and from the base station  30  to the base station  40 .  
         [0064]     This ensures minimal delays in each base station  10 ,  20 ,  30 ,  40  during data transmission, because a reservation of resources and the corresponding granting procedure is performed timely in advance to the data transmission itself so that usually there is no delay as with prior art systems in which each base station individually schedules its resources.  
         [0065]     After issuing the scheduling information  210 , the base station  10  also issues a grant  201  to the subscriber station  13  thus notifying the subscriber station  13  about the time and further parameters of the data transmission such as reserved resources and the like.  
         [0066]     Consequently, after receiving the grant  201  within the subscriber station  13 , the data transmission is performed without unnecessary delays in the multi-hop fashion as symbolized by the arrows  202   a,    202   b,    202   c  and  202   d  of  FIG. 2 .  
         [0067]     Finally, upon receiving the transmitted data in base station  40 , it is forwarded to the destination network element  50 , which itself may be a subscriber station.  
         [0068]     According to a further advantageous embodiment of the present invention, the scheduling information is provided to a further base  20  station prior to processing, which enables an even faster propagation of scheduling information along the multi-hop path constituted by the base stations  10 ,  20 ,  30 ,  40 .  
         [0069]     According to a further advantageous embodiment of the present invention, the scheduling information comprises information on the amount of data to be transmitted. This enables to timely reserve sufficient resources even in case of large amounts of data to be transmitted.  
         [0070]     According to another advantageous embodiment of the present invention, it is also possible to optimise the scheduling information or the timing information, respectively, by measuring actual delays within subsequent data transmissions from e.g. one base station  10  to another base station  20  and by correspondingly adapting the scheduling information and/or the timing information.  
         [0071]     It is also possible to generate feedback information, which may e.g. be based on the measured delays and which is transmitted from base stations downstream the multi-hop path to base stations upstream the multi-hop path. By enabling the use of feedback information, it is possible to establish a closed-loop control for minimising delays and/or jitter.  
         [0072]     Yet another advantageous embodiment of the present invention comprises a controller (not shown) for distributing said scheduling information among the base stations  10 ,  20 ,  30 ,  40 . The use of such a controller enables bypassing base stations which do not support the inventive method of transmitting scheduling information to further base stations.  
         [0073]     Instead of employing the subscriber stations  11 ,  21 ,  31  for transmitting data from their respective base station  10 ,  20 ,  30 , it is also possible to provide base stations  10 ,  20 ,  30 ,  40  which are capable of directly transmitting data to each other.