Abstract:
In a mobile telecommunication system ( 10 ), a number of user equipments ( 40 - 45 ) may receive multimedia broadcast multicast services. The method for power allocation and user assignment for MBMS services determines any number (K) of user equipments which may be served without complete cell area coverage ( 78 ). For more than K user equipments ( 40 - 45 ) requesting MBMS services, dedicated channels are assigned ( 84 ). For user equipments requesting MBMS service during a broadcast, such user equipment is assigned to the channel (broadcast or dedicated) with the lower power requirement, if power is available. If the user is assigned to the broadcast channel, and power is available, power of the broadcast channel is adjusted ( 108 ). Otherwise, the power of the broadcast channel is increased and no further power is indicated as being available ( 112 ).

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention pertains to power management within mobile telecommunication systems and more particularly for multicast services.  
         [0002]     Mobile telecommunication systems transmit information wirelessly over the air. Power for the transmitted signals is a driving consideration in today&#39;s mobile telecommunication services, since the power varies with the distance between the mobile telecommunication station and the user&#39;s equipment.  
         [0003]     Today multimedia multicast services, which are broadcast wirelessly, require large amounts of power by the telecommunication stations. Typically in such wireless telecommunication systems, common channels are used for system based information and signaling messages to all users. In third generation (3G) telecommunication systems, common channels are being considered for high speed data traffic on the downlink for point-to-multipoint communication in order to provide multimedia broadcast multicast services (MBMS).  
         [0004]     Common or broadcast channels are not power controlled and a fixed amount of power is allocated by the Radio Network Controller to provide 95-98% area coverage of the entire cell. Further, not all mobile users within the cell subscribe to broadcast services. However, mobile users requiring multicast services may be anywhere within the cell. Therefore, coverage for multicast services within the cell must be extended to the edges of the cell. The main advantage of using a broadcast channel is that all users inside the coverage area are automatically covered.  
         [0005]     In one possible approach, the Radio Network Controller (RNC) counts the number of mobile users within a cell who are subscribed to multimedia services. If the number of such mobile users in the cell is below a threshold, multimedia services are provided using—dedicated radio channels. Otherwise, the services are provided using the broadcast channel for 98% area coverage reliability regardless of where the mobile users are located and whether these users are subject to fading conditions. When the broadcast channel is used, there must be sufficient power for the broadcast channel to provide multicast services for the coverage of the entire cell. Simulation and field test results show that for 98% area coverage reliability, that approximately 15% of the base station power should be allocated to the common channel for data rates of 64 kbps at 1% frame erasure rate. For a 128 kilobits per second data transfer rate, more than 30% of the total power of the base station should be allocated to the common channel.  
         [0006]     As a result, it would be advantageous to have a multimedia service implementation where only a subset of the users is served by the broadcast channel with the remainder served by dedicated channels. Partial cell coverage reduces the required broadcast channel power significantly, while the remaining users, when selected appropriately, are better served via dedicated channels.  
         [0007]     Accordingly, it would be highly desirable to have a method for assigning multicast users to either dedicated or broadcast channel that minimizes the power required by the base station for supporting multimedia broadcast multicast services.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a block diagram of a mobile telecommunication system including a radio network controller in accordance with the present invention.  
         [0009]      FIGS. 2-4  are a flow chart for power allocation for a radio network controller in accordance with the present invention.  
         [0010]      FIG. 5  is a flow chart for power allocation for a user equipment in accordance with the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0011]     Referring to  FIG. 1 , a mobile telecommunication network  10  is shown. The radio network of the mobile telecommunication system  10  includes a radio network controller  20  and Node Bs  30  and  35 . Radio network controller (RNC)  20  is coupled to radio sites or Node Bs (several Node B N-base stations (Node B))  30  and  35  by a number of links  21 ,  22 ,  24 - 27 . Radio network controller (RNC)  20  controls the switching between Node Bs  30  and  35  and other telecommunication systems or networks (not shown). Node Bs  30  and  35  are each shown, by example, as having three cells, although many more cells may be served by each Node B.  
         [0012]     Each Node B  30  and  35  includes antennas and interface equipment for coupling various user equipment (UE)  40 - 45  to the RNC  20  and the telecommunication networks worldwide. Cell  1  of Node B  30  has three distinct user equipments  40  coupled over the air via links  21  wirelessly to the RNC  20 . Similarly, cell  2  of Node B  30  has three user equipments  41  coupled via links  22  to RNC  20 . These couplings are point-to-point connections That is, one data channel exists for each user equipment from RNC  20  through Node B  30  to the particular user equipment of groups  40  or  41 , for example. The wireless links from cell  31  to UEs  1 - 3  and cell  2  to UEs  4 - 6  are set up as point-to-point connections since at a particular time there may be an insufficient number of user equipments to justify a multicasting arrangement. Each of the users are assumed to be receiving multimedia broadcast services via the user equipment  40 - 45 . Point-to-point connections as demonstrated by cells  31  and  32  to user equipments UEs  40  and  41  respectively increase the overhead on the links  20  and  21 . These point-to-point connections of cells  31  and  32  to user equipments  40  and  41  are made because the number of users, three for each cell, is relatively small.  
         [0013]     For larger groups as shown for cell  33  of Node B  30  and user equipment  42  which includes seven users, a point to multipoint configuration is shown for the multimedia broadcast. That is, since each of the user equipments  42  is receiving the same multimedia broadcast, one link between RNC  20  and cell  33  of Node B  24  is established. Similarly, for larger user equipment groups  43 ,  44  and  45 , the RNC  20  established point-to-multipoint links  25 ,  26  and  27  respectively which couple the RNC  20  to cells  36 ,  37  and  38  of Node B  35 . Cells  36 ,  37  and  38  then perform a point-to-multipoint broadcast to each of the user groups  43 ,  44  and  45  respectively. User equipment  43  includes seven user equipments, user group  44  includes seven user equipments and user group  45  includes seven user equipments. The point-to-multipoint broadcasting achieves certain economies if the number of user equipments is relatively high.  
         [0014]     For Node B  30  there were three links or transport bearers in each group  21  and  22  and a point-to-multipoint link  24  for a total of seven transport bearer links. This is contrasted with three transport bearer links  25 - 27  shown coupling RNC  20  to Node B  35 . As a result of the point-to-multipoint configuration more user equipments were served twenty-one versus thirteen in Node B  30 . Furthermore, bandwidth consumed by the transport bearer links  21 - 24  and  25 - 27  shows a reduction of about 50% in the configuration depicted by Node B  35  and user equipments  43 - 45  over Node B  30  and user equipments  40 - 42 .  
         [0015]     In a preferred embodiment this method uses common channel and dedicated channels simultaneously with a power allocation method that corresponds to the propagation environment and location (geometry) of the user equipment. This method minimizes the power allocation requirement of the broadcast channel by using parameter of cell size and propagation environment. Since the broadcast channel provides only partial coverage of the cell, the user equipment is configured with the parameters defining the coverage area. Then the user equipment notifies the RNC when the user equipment is outside the coverage area. In response, the radio network controller (RNC) either modifies the coverage area or allocates dedicated channel resources to provide the multicast services depending on the location of other user equipment (UE) which subscribes to this service. This method allows a network operator the flexibility to set the percentage of area coverage for a cell where the broadcast channel will be received reliably while reducing the interference in a soft handoff region. This method is particularly well suited for mobile telecommunication systems which are populated by relatively low mobility users. Referring to  FIGS. 2-4  a flow chart of a power allocation method performed by the radio network controller (RNC) is shown. The goal is to assign users to the common or dedicated channel in order to minimize the total transmit power.  
                 P   B     +       ∑     i   =   1     K     ⁢     P   i         ≤     P   EDGE             Equation   ⁢           ⁢   I             
        P B  Power allocated to the broadcast channel for the partial cell coverage     P i  Power allocated to the dedicated channel in SHO     P EDGE  Power required for the common channel to the edge of the cell        
 
         [0019]     For common channel power allocation the power allocation method is started and block  50  is entered. The radio network controller (RNC)  20  selects a default coverage area for the multimedia broadcast multicast service. Then based on system parameters such as the total system power available, the power is allocated to the MBMS function by the network operator. The RNC derives the MBMS coverage threshold, block  52 . Next, the RNC broadcasts the coverage or SNR threshold to the user equipments  40 - 45  which are joining the MBMS service, block  54 .  
         [0020]     The user equipments that joined the MBMS service will measure the S/N based on the received pilot signal and compares to the broadcast SNR threshold. Referring to  FIG. 5 , a user equipment portion of the power allocation method is shown. Once the RNC has sent the coverage threshold to the UE, the method as described in  FIG. 5  is started by each UE. First, each user equipment determines whether a measurement timer has expired, block  60 . If the measurement timer has not expired, control is transferred via the no path block back to block  60  to check again. If the measurement timer has expired, block  60  transfers control to block  62  via the yes path.  
         [0021]     Block  62  resets the measurement timer of the UE. Next the UE measures the S/N of the signal on the common pilot channel, block  64 . Then each UE compares the measured S/N of the common pilot channel with the S/N of the coverage threshold transmitted by the RNC. If the measured S/N is not less than the S/N of the coverage threshold, block  66  transfers control via the no path back to block  60  to iterate the process. If the measured S/N of the common pilot channel is less than the S/N of the coverage threshold, block  66  transfers control to block  68  via the yes path. Lastly, each UE then transmits the measured S/N of the common pilot channel back to the RNC, block  68 . The process is then iterated.  
         [0022]     Referring again to  FIGS. 2-4 , block  56  collects the measurements reported by each of the UEs as to the measured S/N of the common pilot channel signal. Block  56  receives the measured pilot channel signal via a dedicated channel or a random access channel depending upon the state of the UE.  
         [0023]     Next block  58  determines whether the MBMS service is in progress. If the MBMS service is not in progress, block  58  transfers control to block  70  via the no path.  
         [0024]     Next the RNC compiles all the S/N measurements from each of the UEs wishing to join the MBMS service, block  70 . Next, block  72  determines whether -MBMS service is about to begin. If not, block  72  transfers control back to block  72  to iterate the compilation of the received signal to noise ratios from subscribing UE&#39;s. If MBMS service is about to begin, block  72  transfers control to block  74  via the yes path.  
         [0025]     Then the RNC determines the coverage area for MBMS services, block  74 . Then the RNC sorts the measured S/N of each of the UEs from strongest to weakest measured signal, block  76 .  
         [0026]     Then the RNC determines the number of users (K) to support on the broadcast or common channel by Equation II, block  78 .  
             K   =       arg   k     ⁢           ⁢     max   ⁡     (         P   B     ⁡     (     N   UE     )       -       P   B     ⁡     (   k   )       -     (       ∑     i   =     k   +   1         N   UE       ⁢     P   i       )       )                 Equation   ⁢           ⁢   II             
        where P B (k) is the required power of the broadcast channel to support user k, and P i  is the required power to support user i using a dedicated channel. N ue  is the total number of UEs requesting MBMS services. K+1 is the identity of the UE with the S/N which is unable to be supported on the broadcast channel.        
 
         [0028]     Next, the RNC assigns UEs ranked 1 through K to the broadcast channel, block  80 . This ranking is based upon the reported and measured S/N of the common channel pilot signal. If K user equipments are the total number of UEs requesting MBMS service, all the UEs will be assigned by the RNC to the broadcast channel, block  82 .  
         [0029]     Next, the RNC determines whether there are sufficient dedicated channels for users K+1 through the total number of user equipments requesting MBMS service. If there are sufficient dedicated channels the balance of the users greater than K are assigned dedicated channels, block  84 . Next, the RNC sets a new S/N threshold coverage to be the measured S/N of the Kth user equipment, block  86 . Next, the RNC retains the broadcast channel power to be less than the maximum power allocated for MBMS services by the network operator, block  88 . The RNC next sets the broadcast channel power according to the power required for the K th UE, block  90 . The additional power which is available for MBMS service is then given by Equation III.  
               P     B   ,   AVAIL       =       P     B   ,   MAX       -     (       ∑     i   =     K   +   1         N   UE       ⁢     P   i       )     -       P   B     ⁡     (   K   )                 Equation   ⁢           ⁢   III             
        where P B,MAX  is the maximum power that may be assigned to the MBMS broadcast channel (normally assigned by the operator). This maximum is usually the power required to cover the entire cell. N ue  is the total number of UEs requesting MBMS services. K+1 is the identity of the UE with the S/N which is unable to be supported on the broadcast channel.        
 
         [0031]     Lastly, the RNC transmits the new S/N coverage threshold to each of the requesting user equipments, block  92 . Then control is transferred to block  54 .  
         [0032]     Referring again to  FIG. 2 , if the MBMS service is in progress, block  58  transfers control via the yes path to block  100 . If the MBMS service is in progress and the particular UE requesting to be added to the service requires additional power. Depending on the power requirement this particular UE the RNC may not be able to service the request. Next, the RNC determines the power requirement for this particular UE which is requesting MBMS service on the broadcast channel, block  100 . Next, the RNC determines the power requirements for this particular UE on a dedicated channel, block  102 . The RNC then assigns the newly requesting UE to a channel with the smaller power requirement, block  104 . That is either the broadcast channel or a dedicated channel is assigned based upon which channel will require less power to provide the MBMS service to the new UE.  
         [0033]     Next, block  106  determines whether the particular UE is assigned to the broadcast channel with sufficient power available. If the UE is assigned to the broadcast channel block  106  transfers control to block  108  via the yes path. Then the RNC increases broadcast channel power for the new UE and correspondingly decreases the total available power for MBMS services, block  108 . For increasing the broadcast channel power Equation IV is used. 
 
 P   B ( K )= P   B ( K )+ P   ΔB ( i )  Equation IV 
 
         [0034]     For decreasing the total available MBMS power, this is performed by setting the power according to Equation V. 
 
 P   B,AVAIL   =P   B,AVAIL   −P   ΔB ( i )  Equation V 
 
         [0035]     The RNC sets the S/N for the coverage threshold to the measured S/N of the new UE, block  110 .  
         [0036]     Lastly, the RNC assigns the new UE to the broadcast channel and broadcasts a new S/N coverage threshold to each of the UEs receiving the MBMS service, block  116 .  
         [0037]     If there is insufficient power on the broadcast channel to assign the new UE, block  106  transfers control to block  112  via the no path. If the required power for the new UE is greater than the available MBMS power, the RNC increases the power on the broadcast channel and decreases the available MBMS power to zero, block  112 . For increasing the power according to block  112  the Equation VI is used to make the determination. 
 
 P   B ( K )= P   B ( K )+ P   B,AVAIL   Equation VI 
 
         [0038]     For decreasing the available MBMS power, Equation VII is performed. 
 
 P   B,AVAIL =0  Equation VII 
 
         [0039]     Next, the RNC sets the new S/N coverage threshold to the S/N corresponding to the maximum power for the MBMS service allowed by the system operator, block  114 .  
         [0040]     Lastly, the RNC assigns the new UE to the broadcast channel and broadcasts a new S/N coverage threshold to all of the UEs, block  116 . Then block  116  transfers control to block  54 .  
         [0041]     In previous technology for implementing broadcast channels for MBMS services, power sufficient for the broadcast channel was required to the edge of each cell. This put a tremendous burden on the power allocated for the MBMS function and for the overall power of a mobile telecommunication system and network.  
         [0042]     In an embodiment of this invention, partial broadcast channel coverage is provided thereby significantly reducing the power required for the broadcast channel. Dedicated channels are assigned to user equipment which is on the edge or fringe of a cell. Using an embodiment of the present invention for providing an 80% MBMS service coverage area within a cell only uses about 2.5% of the total Node B&#39;s power.  
         [0043]     Although the preferred embodiment of the invention has been illustrated, and that form described in detail, it will be readily apparent to those skilled in the art that various modifications may be made therein without departing from the spirit of the present invention or from the scope of the appended claims.