Abstract:
Methods and apparatus relate to cellular communications and in particular to a frequency spectrum shared by two cellular networks. An object is flexible utilization of the spectrum. This is achieved by a method where a first of the networks occupies part of the shared spectrum in relation to the traffic load in the first network. The first network informs a second of the networks on the extent the shared spectrum is occupied, for the second network to be free to use the shared spectrum outside the occupied part. A radio resource management unit, a base station controller, and a radio base station are also disclosed. An advantage is that spectrum can be lent from an old system when a new system is introduced.

Description:
[0001]    This application is a continuation of and claims the benefit of the filing date of U.S. patent application Ser. No. 12/522,510 filed on Jul. 8, 2009, which is a 371 of International Application PCT/SE2007/050019 filed on Jan. 15, 2007, both of which applications are incorporated here by reference. 
     
    
     TECHNICAL FIELD OF THE INVENTION  
       [0002]    The present invention relates to cellular radio communications in general and more particular to a method for utilizing a frequency spectrum band shared among two or more radio networks. The invention also relates to a control node for performing the method, to an RRM node, to a base station controller and a radio base station comprising the RRM node. 
       DESCRIPTION OF RELATED ART 
       [0003]    In traditional planning of cellular networks, a range of contiguous radio frequencies, referred to as a carrier, are allocated in a static fashion to a single radio network. This is illustrated with the frequency axis in  FIG. 1 , where Carrier  1 , ranging from frequency f 1  to f 3 , is allocated to Cellular Network.  1  and Carrier  2 , that ranges from frequency f 2  to f 4  is allocated, to Cellular Network  2 , Between the two carriers, a Guard-Band is typically included in order to reduce the spurious emissions emitted between the cellular networks. 
         [0004]    As a consequence of this traditional deployment the traffic belonging to cellular network  1  is kept entirely in carrier  1  and the traffic belonging to cellular network  2  is kept entirely in carrier  2 . 
         [0005]    Since there is no overlap between the two carriers decisions about the scheduling of data on carrier  1  can be taken by cellular network  1  without any information about the scheduling of cellular network  2  and vice versa. One example of the above is where cellular network  1  is a GSM network belonging to operator A and cellular network  2  is a GSM network belonging to operator B. Another example will be when cellular network  1  is a GSM network and network  2  is an LTE network and the two networks  1  and  2  belong to the same operator. This is illustrated in the time/frequency axis of  FIG. 2 . 
         [0006]    Operators will need an increased flexibility in their cellular deployments in the coming years for several reasons:
       An increased number of cellular technologies ate available   The need to migrate spectrum from their currently deployed cellular technology (e.g. GSM) to more modern cellular technology (e.g. LTE).   Shortage of spectrum will certainly be a problem for some operators, it is often expensive to get access to.   A general trend of “technology agnosticism” from regulators, whereby the allocation of frequency bands to operators does not prescribe the usage of any particular technology.       
 
       SUMMARY OF THE INVENTION  
       [0011]    The object of the present invention is flexible utilization of a spectrum by two networks. 
         [0012]    In the first radio network an RRM unit control the radio resource management in one or more cell, and in the second network a second RRM unit controls the radio resource management in one or more cell. The basic concept of the invention is to occupy part of a spectrum for use in the one or more cell/s controlled by the first RRM unit in relation to the traffic load in the cell/s controlled by the first RRM unit. The second RRM unit is informed of the occupied part of the shared spectrum, and is free to use the shared spectrum outside the occupied part. 
         [0013]    The invention also relates to a first RRM unit with an interface for connection to the second RRM unit, and that has means for performing the method. 
         [0014]    The invention further relates to a base station controller, and a radio base station including the RRM unit. 
         [0015]    An advantage with the invention method is a superior utilization of the shared spectrum. 
         [0016]    In particular it is an advantage when a new network based on new technology is introduced. The frequency band dedicated to the new network may be too narrow to allow for the highest bitrates affordable by the technology itself. The frequencies of the shared spectrum then make the highest bitrates possible. 
         [0017]    A further advantage exampled by the GSM and LTE networks is that that the average bitrates in the LTE system, as seen by the end-user, are substantially higher than they would be if LTE was confined to a part of the spectrum that is dedicated to the LTE-network only. 
         [0018]    Yet another advantage of the invention is a radio network that is shared between two different network operators. In this embodiment two operators may share one RBS. At least one part of the spectrum in which the RBS operates its radio communication is then shared between the two operators so that the RBS can use the shared part of the spectrum either for radio communication to mobile stations attached to the first network operator or for radio communication attached to the second network operator. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a frequency axis illustrating the prior art usage of the spectrum bands. 
           [0020]      FIG. 2  is the same as  FIG. 1 , except for illustrating an inventive usage of spectrum. 
           [0021]      FIG. 3  is a time/frequency diagram illustrating spectrum utilization of two separate bands by a GSM and an LTE network. 
           [0022]      FIG. 4  is the same as  FIG. 2 , whereas illustrating an alternative spectrum utilization. 
           [0023]      FIG. 5 , is a view of some nodes, and cells of two Networks. 
           [0024]      FIG. 6  is a block diagram of nodes in a GSM and an LTE system. 
           [0025]      FIG. 7  is a flowchart of the steps of a first method embodiment 
           [0026]      FIG. 8  block diagram of nodes in a GSM and an LTE system and a control node. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0027]    The invention is based on a frequency band being divided into tree part, as is depicted by the frequency axis in  FIG. 2 , The frequency band f 1 -f 2  is allocated to a first network, the frequency band from f 3 -f 4  is allocated to a second network, albeit part f 3 -f 2  of the allocated bands are shared by both networks and the first network has only a part f 1 -f 3  of carrier dedicated for its own and the second network only part f 2 -f 4  of carrier dedicated. In the lower part of  FIG. 2  the respective RRM (Radio Resource Manager) of the networks are marked by boxes. The RRM control the usage of the spectrum and are connected for communicating the usage of the shared spectrum between each other. 
         [0028]    The core of the invention is the exchange of information messages between the first and the second network which allows each system to know which part of the shared spectrum that is eligible for traffic scheduling. These information messages can be either proprietary or standardized. 
         [0029]    The advantage of the spectrum allocation can be understood by comparison of  FIG. 3  that discloses prior art allocation a spectrum to a GSM and an LTE net, and its usage by the GSM traffic in a time/frequency diagram, with the spectrum allocation and usage in  FIG. 4 , illustrating the inventive allocation to the nets in the same type of diagram. To maintain an acceptable grade of service, i.e. a low blocking rate, the operator is forced to allocate bandwidth to GSM for traffic peaks to be handled within the spectrum allocation. With static spectrum allocation, as in the prior art, this limits the bandwidth allocation to LTE. By sharing part of the spectrum the LTE system can get access to it, and get a large part of it, during the time periods when the traffic in GSM is low or medium. Thereby the LTE can offer a substantially larger capacity and peak rate. 
       FIRST EMBODIMENT 
       [0030]    The inventions primary application is for scenarios where both networks belong to the same operator. 
         [0031]      FIG. 5 , is a view of a first cell C 1  in a GSM system and a second cell C 2  in an LTE system. The first cell C 1  is served by radio base station  15  in the GSM system, i.e. a GSM BTS,  15 , and the second cell C 2  is served by an LTE RBS  12  (radio base station). The GSM BTS,  5 , is connected to a GSM BSC (Base Station Controller)  13 . The GSM BSC,  13 , and the LTE RBS,  12 , have links for data communication via a core network. For this invention the links are not important. Important is instead, a new link connecting the GSM BSC,  13 , with the LTE RBS  12 , and that will be described further down. 
         [0032]    Of course GSM and LTE networks comprise numerous cells and base stations  15 ,  12 .  FIG. 5  is for illustrative purposes of two networks, controlled by the same operator, sharing part of spectrum and having at least some cells with overlapping geographical coverage as is the case with the first and the second cell C 1 , C 2 . This complicates the interference situation. 
         [0033]      FIG. 5  is a block diagram, illustrating functional blocks of the GMS BTS  5 , the GSM BSC,  13 , and the LTE RBS,  12  that are essential for the invention. 
         [0034]    The functional blocks in the GSM BSC,  13 , are the GSM radio resource manager  2 , the Channel handler  3 , the group switch  4  and the signaling entity  6  that communicates with the LTE system via the LTE signaling entity  7 . The GSM BTS,  5 , includes the important modules Radio unit  5  and antennas. The LTE RBS contains the functional blocks Signaling Entity  7 , radio resource manager  8 , the Scheduler  9 , the data buffer  10 , the radio unit  11  and the antennas. The functional blocks of the GSM BSC,  13 , and LTE RBS,  12 , are with exception of the radio unit  11 , primarily implemented as software executed by processors. They may however to a various extent be implemented by hardware. The extent is choice of implementation. The functional units,  2 - 4 ,  6 - 11 , are typically implemented in separate physical program and processors, however some of the functional units may share physical entity. 
         [0035]    In the first embodiment the GSM system has priority in the snared spectrum but lets the LTE system know, by means of the information elements sent between from the GSM RRM,  2 , to the LTE RBS RMM,  8 , which parts of the shared spectrum are used by GSM and when. The LTE system would then maintain up to date information about which part of the shared spectrum is presently occupied by GSM and schedule LTE data in the remaining part of the spectrum. This function will be described in more detailed with reference to  FIG. 6  and to the steps of a method illustrated by the flowchart of  FIG. 7 . 
         [0036]    The GSM RRM,  2 , controls both the spectrum that has been dedicated to GSM only, i.e. the carrier between frequencies f 1  and f 3  in  FIG. 2 , and the spectrum that has been allocated to both GSM and LTE, i.e. the shared spectrum between frequencies f 3  end f 2  in  FIG. 2 . 
         [0037]    Initially the GSM REM,  2 , takes frequencies from the shared spectrum into use based on the traffic load in the GSM network, see S 1  in  FIG. 7 . 
         [0038]    In following step S 2 , the GSM RRM,  2 , signals to the GSM signaling entity,  6 , what frequencies in the shared carrier are presently in use by the GSM radio network. The GSM signaling entity,  6 , sends an information element containing this information to the LTE signaling entity which forwards this message to the LTE RRM,  8 . 
         [0039]    In S 3 , the LTE RRM  8 , processes the information with other available information about which frequencies to use and sends the resulting radio resource information to the LTE scheduler,  9 . In particular the LTE RRM,  8 , instructs the scheduler,  9 , not to use any of the frequencies in the shared carrier that is presently being occupied by GSM. The LTE scheduler,  9 , uses this information in combination with other available data to determine which user data in the data buffer,  10 , shall be transmitted to the mobile stations and which resources, such as frequencies, shall be used. In particular the scheduler,  9 , uses only the frequencies that are indicated as available by the LTE RRM,  2 . 
         [0040]    The traffic load of the GSM is monitored, S 4 , and compared to upper and lover thresholds, S 5 . This is performed by the GSM RRM,  8 . 
         [0041]    In case of a decrease in the GSM traffic load, the first step is again entered by the GSM RRM,  2 , releasing some of the frequencies occupied by GSM. The steps following on the first step S 1  is performed in a loop. 
         [0042]    In an alternative step  4  and  5 , S 4 , S 3 , the channel handler,  3 , receives a request for a new voice call to be set tip in the GSM cell. The channel handler,  3 , signals this request to the RRM,  2 , which determines traffic load increase. 
         [0043]    If step  5 , SS, results in a increase of the GSM load, the GSM RRM,  2 , in a sixth step S 6 , identifies a GSM radio channel that can be used and stores information about which frequencies that GSM channel requires. The GSM radio resource manager sends a message to the LTE resource manager. The message contains information about the frequencies that are going to be used for the GSM call and instructs the LTE system to not use these frequencies for scheduling traffic. 
         [0044]    The LTE RRM,  8 , acknowledges receipt of the information, and the acknowledgement is received by the GSM RRM,  2 , the seventh step S 7 . 
         [0045]    Next, see S 8 , the GSM RRM,  2 , grants the channel handler to set up the voice call on the identified frequencies. The channel handler,  3 , uses state of the art methods to set up the voice call through the group switch over the abis interface via the GSM BTS,  5 , and over the radio interface to the motile using the radio channel granted to the call by the GSM REM. In parallel, to the voice call set up, the LTE signaling entity,  7 , informs the LTE RRM about the frequencies that are from now on used for the GSM voice call. The LTE RRM relays this information to the LTE scheduler which immediately stops all scheduling on the corresponding frequencies. 
         [0046]    When the last step is performed the traffic in the GSM system is monitored, see step S 4 , and the further steps are performed in a loop. 
       SECOND EMBODIMENT 
       [0047]      FIG. 8  is block diagram, of the same nodes as  FIG. 6  with the exception of a control node,  14 , external the GSM and LTE network nodes. The control node,  14 , has interfaces connecting to the signaling entities,  6 ,  7 , of the GSM BSC,  13 , and LTE RBS,  12 , via links  21 . All the functional units,  2 - 4 ,  6 - 15 , of the GSM BSC,  13  and the LTE RBS,  12  are the same as in  FIG. 6 , albeit the functioning of the RRMs being somewhat different. 
         [0048]    In the second embodiment, the GSM is not privileged over the LTE in the access to the shared network. The LTE RRM,  8 , monitors the traffic load and if the load cannot be handled within the frequency spectrum already assigned by the control node,  14 , the LTE RRM,  8 , requests the control node,  14 , to assign more of the shared spectrum to the LTE system. The GSM RRM,  2 , functions in the same way. The request on spectrum allocation from the LTE and GSM RRM,  2 ,  8  includes a measure of the respective the traffic load. 
         [0049]    When the control node,  14 , has received the request, to be assigned more of the shared spectrum from the LTE RRM,  8 , the control node,  14 , request the GSM RRM,  2 , to provide a measure of the GSM traffic load. The control node,  14 , compares the traffic loads of the GSM and LTE networks. 
         [0050]    Based on the information about the load in the GSM and LTE networks respectively, present spectrum allocations and policies as defined by the network operator the control node,  14 , decides whether or not the present allocations of the shared spectrum to the GSM REM function and LTE RRM functions shall foe changed. If the decision of the RRM control node,  14 , is to re-assign (change) then both the RRM,  2 ,  8  of the GSM and LTE networks are informed. If the decision is to do no re-assignment, then only the LTE RRM,  8 , is informed because it made the request. 
       Traffic Load Measures and Policy Parameters 
       [0051]    The control node,  14 , in the second embodiment need to compare the traffic load measures from the LTE and GSM systems. The measures should be processed by the respective RRM,  2 ,  8 , to be comparable. The measures could for example be based on any of the parameters: occupation of available radio channels, packet loss over radio, delays, throughput in either the uplink or downlink direction or any combination of the parameters. Preferably, the measure is quantified in relation to the frequencies already assigned. 
         [0052]    The load measures can be either of the form of instantaneous load level, load level as filtered over a well-defined time period which could range from milliseconds to minutes or even hours. Alternatively the load measures could be predictions of the load situation for a future time period. 
         [0053]    The load measures could be sent periodically frost the RRM units  2  and  8  to the central RRM control function  14 . Alternatively the load measures could be sent based on events, e.g. a significant change in the load situation in either of the GSM and LTE system as compared to last reported load measure. the policy parameters serve the purpose to compare end weigh the importance of the load measures in the decision about how to re/assign spectrum to the RRM units  6  and  8 . The policy parameters are either a permanent part of the RRM control unit  14  or provisioned to the RRM control unit  14 , e.g. by means of an operation and management system. The policy parameters could e.g. compare two conceptually different load measures such as number of ongoing voice calls in GSM to the channel occupancy of LTE or weigh two comparable measures such as channel occupancy in the two systems. In one embodiment of the invention the policy parameters are used to prioritize one network, over the other which in the extreme limit of absolute priority to GSM gives a function similar to embodiment one of the invention discussed in previous sections. 
         [0054]    The policy parameter can also be connected to QoS (Quality of service) policies of the individual end-users in the two systems so that spectrum is assigned based on services and individual user priorities. 
       Further Alternatives to the Embodiment 
       [0055]    It should be understood that the RRM,  2 , of the GSM system could be connected to plural RRM,  8 , in respective LTE RBSs,  12 . Thereby, the GSM RRMs,  2 , could be connected to a number of LTE RBS,  12 , that correspond in number and geographical coverage to a number of GSM BTS,  15 , that are controlled by the GSM BSC,  13 . 
         [0056]    The GSM and LTE networks are examples of networks used in the first and second embodiment. Networks based on other radio access technologies can of course be used in combination with the present invention. For example the invention would be advantageously when migrating from a network based on CDMA technology to a network based on OFDM or any other future access technology. The RRM,  2 , or the control node,  14 , could further allocate the uplink and the downlink spectrum separately. 
         [0057]    Other systems may divide there functional entities differently than that of the GSM. BSC, and give other names to the entities. 
         [0058]    The networks sharing a spectrum could also be based on the same access technology. This is in particular the case for the scenario when the control node,  14 , assigns the shared spectrum to a network that offers the highest price for access the shared spectrum. Moreover, it could be possible to share a spectrum by more than two networks. 
       ABBREVIATIONS 
       [0059]    LTE Long Term Evolution of 3 G as is standardized by 3GPP 
         [0060]    OFDM Orthogonal Frequency Division Multiple Access 
         [0061]    RBS Radio Base Station 
         [0062]    RRM Radio Resource Manager 
         [0063]    BTS Base Transceiver Station