Abstract:
The present invention relates to methods and arrangements for improving the capabilities of an evolved Universal Terrestrial Radio Access Network, in particular for cases when more than one radio access network applying a time-division duplex transmission mode need to co-exist on a same carrier. The invention addresses further problems concerning an efficient allocation of uplink resources and resource allocation in a handover situation. The present invention assigns an attribute in form of a distinguishing value to the time slots used for the uplink and downlink transmission on said carrier such as to avoid scheduling of transmissions via a first radio access network in downlink or uplink time slots assigned to the second radio access network and to avoid scheduling of transmissions via the second radio access network in uplink time slots assigned for transmissions in the first radio access network.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to methods and arrangements in a telecommunication system, in particular to improvements in an evolved Universal Terrestrial Radio Access Network (E-UTRAN. 
       BACKGROUND 
       [0002]    The development of E-UTRAN shall ensure competitiveness of future mobile communication systems in a long-term perspective, i.e. 10 years and beyond. The overall target is to further reduce operator and end-user costs and to improve service provisioning. Possible ways of reaching this target are to study ways to achieve reduced latency, to achieve higher user data rates, and improve the system capacity and coverage. One of the main novelties introduced for E-UTRAN in order to achieve these targets is the introduction of a new physical layer. This new physical layer applies Orthogonal Frequency Division Multiplexing (OFDM) for the downlink and Single Carrier Frequency Division Multiple Access (SC-FDMA) for the uplink. These choices were made, e.g., to achieve greater spectrum flexibility and enabling deployment in various spectrum allocations; to achieve the possibility of frequency domain adaptation and enabling higher spectrum efficiency; to achieve enhanced efficiency for broadcast services in the downlink due to the inherent macro-diversity combining properties of OFDM; and to achieve reduced receiver complexity, especially at high bandwidths and in conjunction with MIMO. 
         [0003]    An evolved UTRAN can apply either a frequency-division duplex (FDD) transmission mode or a time-division duplex (TDD) transmission mode. When applying the time-division transmission mode, the evolved UTRAN uses the same frequency band for both uplink and downlink communication. Thus, some time slots are reserved for the uplink while others are reserved for the downlink. This is typically configured by the network. One time slot is assigned mandatory for the downlink, e.g. the first time slot in a radio frame. By reading control information in this time slot, the UE then knows the configuration of the other time slots, uplink or downlink. 
       SUMMARY 
       [0004]    The present invention addresses problems that occur when more than one radio access network applying a time-division duplex transmission mode, e.g. UTRAN and E-UTRAN, need to co-exist on a same carrier. The invention addresses further problems concerning an efficient allocation of uplink resources and resource allocation in a handover situation. 
         [0005]    It is thus the object of the present invention to improve the capabilities of an evolved Universal Terrestrial Radio Access Network coexisting with a normal Universal Terrestrial Radio Access Network. 
         [0006]    It is the basic idea of the present invention to assign an attribute in form of a distinguishing value to the time slots used for the uplink and downlink transmission on said carrier such as to avoid scheduling of transmissions via a first radio access network, e.g. the UTRAN, in downlink or uplink time slots assigned to the second radio access network, e.g. the E-UTRAN, and to avoid scheduling of transmissions via said second radio access network in uplink time slots assigned for transmissions in said first radio access network. 
         [0007]    The present invention thus implies the advantage to provide a radio base station node that is capable to handle transmissions of more than one radio access network applying a time-division duplex transmission mode and using a same carrier. Correspondingly, user equipments applying a time-division transmission mode can be used in areas with co-existing radio access networks applying time-divided transmission on a same frequency carrier. 
         [0008]    The present invention further implies the advantage of a more efficient resource allocation to user equipments connected to said radio base stations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0009]      FIGS. 1   a  and  1   b  illustrate the present invention according to the second improvement. 
           [0010]      FIG. 2  shows an example communication network within which the present invention can be applied. 
           [0011]      FIG. 3  illustrates a network node, e.g. a radio base station, according to the present invention. 
           [0012]      FIG. 4  illustrates a user equipment according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]      FIG. 2  illustrates a part of an E-UTRAN comprising radio base stations  21 , 25  (or evolved NodeB, eNB) that is connected to a core network  24  via an interface node  23  and provides communication services to user equipments  22 . The radio base station  21  can be equipped to also serve in another radio access network, e.g. a UTRAN. 
         [0014]    One aspect of the present invention addresses problems when transmissions on an evolved UTRAN and another radio access network, e.g. a UTRAN or “pre-LTE”-system, need to coexist on a same carrier. Transmissions via the UTRAN system shall not be allowed on uplinks assigned to the E-UTRAN. This is obtained by configuring the uplink time slots assigned to the UTRAN only for those instances when an uplink transmission on the UTRAN is supposed to happen. The other time slots are assigned for UTRAN downlink, E-UTRAN uplink, or E-UTRAN downlink. The network can thus avoid scheduling of transmissions via the UTRAN in the downlink time slots of the E-UTRAN. This also applies vice versa, i.e. transmissions via the E-UTRAN do not transmit in uplink time slots assigned to the UTRAN. A terminal that is configured for communication via the UTRAN may listen for the downlink channels also in time slots that are supposed for the downlink of an E-UTRAN. The mobile may thereby, unintentionally, find signaling that relates to the communication on the E-UTRAN and obey to the content of this signaling. Therefore, the present invention introduces an attribute for each time slot carrying distinguishing values. 
         [0015]    For instance, three values can be applied: ‘UL’, ‘DL’, and ‘DTX/DRX’. In time slots that are marked as ‘DTX/DRX’ time slots, the user equipment should not listen to any downlink transmission, nor transmit anything on the uplink. 
         [0016]    The same principle of this invention is also applicable for handling synchronous hybrid ARQ (synch HARQ) in the uplink. 
         [0017]    With sync HARQ, retransmissions occur at a predefined uplink time slot. If this time slot is used for other purposes, e.g. random access, it should not be configured as uplink time slot for data purposes. However, it should not be configured as downlink time slot either as this would imply that the user equipment is trying to find control signaling. Hence, it is beneficial to separate the indications of uplink and downlink time slots from each other. 
         [0018]    Regarding guard times, the principle of this invention might be applied to signal three different subframe types to the user equipment (denoted, e.g., “downlink subframe”, “uplink subframe”, “inactive subframe”) which will be beneficial for the coexistence of a UTRAN with an E-UTRAN. Inactive subframes ensure that user equipments that are designed for communication via the UTRAN do not—by mistake—decode control signaling sent on the downlink of the E-UTRAN. 
         [0019]    Further, for synchronous hybrid ARQ it is not always possible to simply “avoid scheduling” as it may be that a sync retransmission takes place. There is therefore a need to signal some kind of information indicating subframes that are available for uplink transmissions to the user equipment. Subframes that are not available for the uplink can be used for the downlink or for random access. The sync HARQ process numbering is done on the UL-available subframes (and may therefore not be an even multiple of the 10 ms radio frame). 
         [0020]    Another aspect of the present invention relates to an efficient allocation of transmission resources. A user equipment can, according to one embodiment of the present invention, take into account the presence of certain types of common control (overhead) channels that are known to be transmitted in some subframes. For instance, BCH, PCH, or FACH will be mapped to the first subframe in a radio frame which is known to both the radio base station node and the user equipment. One subframe carries BCH, PCH, and FACH while others do not. Regarding the uplink, some uplink subframes may contain common overhead channels for random access. As a consequence, some subframes can contain more user data than other subframes. Scheduling control signaling is used to indicate which “data resources” a user equipment is supposed to receive. As it is, however, undesirable to have different scheduling control signaling structures in the different subframes, this embodiment of the present invention applies the a-priori knowledge on subframes containing said overhead channels, either predefined (as for the BCH) or semi-statically configured based on BCH information (as for the PCH or FACH). The user equipment, thus, can take this knowledge into account when interpreting the scheduling control signaling both for downlink and uplink scheduling. There is no need for special control signaling for the first subframe and the user equipment accounts for the presence of BCH/PCH/FACH. For instance, figure la illustrates a series of resource blocks  10  whereof a fraction  11  of said resource blocks, particularly resource blocks  3 - 14 , is assigned to a user equipment by means of control signaling. The user equipment receives and processes the complete fraction of said resource blocks as it knows that no overhead channels use the subframes of said fraction. In the example of  FIG. 1   b , the user equipment uses all resource blocks of said fraction except for resource blocks  4 ,  8 ,  12 , and  16  (selected by means of an illustrating example only) as the user equipment can apply a-priori knowledge that the excepted resource blocks are used for overhead control channels. 
         [0021]    Uplink transmission resources can, according to one embodiment of the present invention be assigned by means of a scheduling grant controlling the uplink transmission that does not point directly to the resources to use for the uplink transmission but indicates which hopping sequence is to be used. As there is no uplink channel-dependent scheduling in the frequency domain, interference diversity is important together with hopping on, e.g., on a 0.5 ms basis. The uplink resources that are used for transmission can be retrieved from a function taking as an input one or more of, e.g., the following: The resources that are assigned by the scheduler, the connection frame number, the cell-ID, or any other appropriate parameter. 
         [0022]    A further embodiment of the present invention relates to resource scheduling for handover access between the radio base station  21  of a source cell and the radio base station  25  of a target cell. After that the radio base station  21  of the source cell has requested handover resources from the radio base station  25  of the target cell, the target cell radio base station  25  allocates resource blocks dedicated to a “handover access”, e.g. periodically occuring resource blocks due to the handover request (i.e. the target cell stops using these resource blocks for own user equipments; although the target cell may also allocate the resources to be used by the new entering user equipment  22  after the handover access phase) . The target cell radio base station  25  adapts its scheduling (if needed) such as to provide that the allocated handover resources will contribute with little interference and are not allocated to own user equipments and indicates then the allocated handover access resources to the source cell radio base station  21 , which in turn indicates the allocated handover access resources to the user equipment  22 . After that the user equipment  22  has moved to the target cell and started to use said handover resources, the target cell radio base station  25  can start scheduling the user equipment  22  according to Qos requirements while the allocated handover resource blocks can be utilized again as normal resource blocks. 
         [0023]      FIG. 3  illustrates a network node  21 , e.g. a radio base station, according to the present invention. The network node  21  is located in a communication system applying a time-division duplex transmission of time slots on a same frequency band for uplink and downlink transmissions to user equipments and support access to at least a first and a second co-existing radio access network. The network node  21  comprises means  211  for assigning to each time slot an attribute distinguishing transmission mode and direction of transmission in said time slot. According to further embodiments of the present invention, the network node  21  can also comprise means  212  for providing signalling information of subframes that are available for the user equipment  22  for uplink transmission and/or means  213  for performing a resource allocation for an uplink transmission by indicating the hopping sequence to be used for said transmission. 
         [0024]      FIG. 4  illustrates a user equipment  22  according to the present invention, said user equipment conncected to a network node  21  applying a time-division duplex transmission of time slots on the same frequency band for uplink and downlink transmissions to said user equipment  22 . The network node  21  supports access to at least a first and a second co-existing radio access network, whereby said user equipment  22  has access via said first radio access network. The user equipment  22  comprises means  221  for retrieving information on an attribute assigned to the time slots of a received transmission from the network node  21  and means  222  for omitting time slots that are marked with a value prohibiting the usage of such time slots to user equipments accessing said network node  21  via the first radio access network. According to further embodiments of the present invention, the user equipment can further comprise means  223  for retrieving information signalled by the network node  21  of subframes that are available for the user equipment  22  for uplink transmission and/or means  224  for determining control channels in certain subframes by applying pre- or semi-statically configured information of said channels in a storage means  225  and deriving an indication of the resource allocation for uplink or downlink subframes by accounting said determined control channel information.