Abstract:
A system for controlling congestion in a code division multiple access system with multi-user detection capabilities is disclosed. The system includes at least one user equipment, a base station, and a radio network controller. Each user equipment includes a receiver having multi-user detection capabilities. The base station includes a receiver having multi-user detection capabilities, an intra-cell interference measuring device, and an inter-cell interference measuring device. The radio network controller includes a radio resource management device configured to control congestion based on measurements taken by the base station.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 12/004,219, filed Dec. 20, 2007, issuing as U.S. Pat. No. 8,605,577 on Dec. 10, 2013, which is a continuation of U.S. patent application Ser. No. 10/265,046, filed on Oct. 4, 2002, now U.S. Pat. No. 7,313,091, issued Dec. 25, 2007, which claims priority from U.S. Provisional Patent Application No. 60/383,025, filed on May 24, 2002, which are incorporated by reference as if fully set forth herein. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to code division multiple access (CDMA) systems with multi-user detection (MUD) capabilities, where the capacity of the system is limited by non-cancelled intra-cell interference, non-cancelled inter-cell interference and interference associated with the noise floor. 
         [0003]    In CDMA systems, one of the factors that limit the capacity of the system is interference. In general, these systems try to generate as little interference as possible. Power control is one approach that is commonly used in order to maintain the interference limits as low as possible. Nevertheless, when a CDMA system attempts to support many users, even if the transmission power is being controlled, the levels of interference may not be acceptable. 
         [0004]    The concept of CDMA uplink (UL) pole capacity has been widely used for evaluating when a system is becoming congested. This concept is based on the exponential growth of interference caused by a CDMA system, i.e. all interference above the noise floor. The interference caused by a CDMA system is made up of intra-cell interference and inter-cell interference. Intra-cell interference is interference generated in a cell that is occupied by a user. Inter-cell interference, in contrast, is interference generated from all sources outside of the cell in which the user is located. The pole capacity is the theoretical maximum capacity assuming the mobiles have infinite available transmitting power. The actual capacity is typically a fraction of the pole capacity. Although the concept generally applies to any point-to-multipoint CDMA system, the use of a MUD in the receiver that cancels some of the intra-cell interference varies the principle on which the concept is based thereby rendering the concept not applicable. 
         [0005]    A method is therefore needed for evaluating congestion in CDMA systems having MUD capabilities. 
       SUMMARY 
       [0006]    A system for controlling congestion in a code division multiple access (CDMA) system with multi-user detection capabilities is disclosed. The system includes at least one user equipment, a base station, and a radio network controller. Each user equipment includes a receiver having multi-user detection capabilities. The base station includes a receiver having multi-user detection capabilities, an intra-cell interference measuring device, and an inter-cell interference measuring device. The radio network controller includes a radio resource management device configured to control congestion based on measurements taken by the base station. 
         [0007]    A system for controlling congestion in a CDMA system with multi-user detection capabilities includes at least one user equipment, a base station, and a radio network controller. Each user equipment includes a receiver having multi-user detection capabilities, an intra-cell interference measuring device, and an intra-cell interference signaling device configured to send a signal that is indicative of intra-cell interference to the base station. The base station includes a receiver having multi-user detection capabilities and an intra-cell interference signal receiver configured to receive the signal sent by the intra-cell interference signaling device. The radio network controller includes a radio resource management device configured to control congestion based on measurements taken by the at least one user equipment. 
         [0008]    A system for controlling congestion in a CDMA system with multi-user detection capabilities includes at least one user equipment, a base station, and a radio network controller. The base station includes a receiver having multi-user detection capabilities, an intra-cell interference measuring device, and an inter-cell interference measuring device. The radio network controller includes a radio resource management device configured to calculate a noise rise value that is indicative of interference in the CDMA system, monitor the noise rise value to detect congestion, and implement congestion relieving measures on a condition that congestion is detected, whereby the radio resource management device controls congestion. 
         [0009]    A system for controlling uplink congestion in a CDMA system with multi-user detection capabilities includes a base station, at least one user equipment, and a radio network controller. The base station includes a receiver having multi-user detection capabilities and an inter-cell interference measuring device. Each user equipment includes a receiver having multi-user detection capabilities, an intra-cell interference measuring device, and an intra-cell interference signaling device configured to send a signal that is indicative of intra-cell interference to the base station. The radio network controller includes a radio resource management device configured to control congestion based on the intra-cell interference signal from the at least one user equipment and the inter-cell interference measured by the base station. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a flow diagram showing a method for monitoring congestion in the UL based on UE measurements for CDMA systems having MUD capabilities in accordance with an embodiment of the invention. 
           [0011]      FIG. 2  is a flow diagram showing a method for monitoring congestion in the UL based on RAN measurements for CDMA systems having MUD capabilities in accordance with an embodiment of the invention. 
           [0012]      FIG. 3  is a flow diagram showing a method for relieving congestion in accordance with an embodiment of the invention. 
           [0013]      FIG. 4  is a system for monitoring and controlling congestion in the UL based on UE measurements in accordance with an embodiment of the invention. 
           [0014]      FIG. 5  is a system for monitoring and controlling congestion in the UL based on RAN measurements in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]    For uplink (UL) congestion detection based on UE measurements, the pole capacity of regular CDMA systems, i.e., CDMA systems not having MUD capabilities, may be determined by measuring the noise rise, which is the ratio of the total perceived interference to noise floor: 
         [0000]    
       
         
           
             
               
                 
                   Noise_rise 
                   = 
                   
                     
                       
                         total_perceived 
                          
                         _interference 
                       
                       noise_floor 
                     
                     = 
                     
                       1 
                       
                         1 
                         - 
                         
                           η 
                           UL 
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
       
     
         [0000]    where the total perceived interference is all non-cancelled interference (both intra-cell and inter-cell) at the receiver, the noise floor is all noise that is unrelated to the system such as the thermal noise, and η UL , is the UL load factor. In CDMA systems having MUD capabilities, however, the MUD reduces intra-cell interference (I or ) and amplifies inter-cell interference (I oc ). Therefore, to accurately measure noise rise in CDMA systems having MUD capabilities, the η UL  should account for the affect the MUD has on interference. 
         [0016]    To specifically account for the effect of the MUD, two parameters (one to account for the decrease in I or  and one to account for the increase in I oc ) are defined and incorporated into η UL . The first parameter,  α   UL  represents the average ratio of the cancelled I or  to the total I or  and is used to account for the decrease in I or . The second parameter,  β   UL , represents the average ratio of received extra I oc  to the total I oc  and is used to account for the increase in I oc . The parameters  α   UL  and  β   UL  may be measured, calculated or assumed, as desired. Using I or , I oc ,  α   UL  and  β   UL , the total perceived interference as affected by the MUD is (1−  α   UL )Ior+(1+  β   UL )Ioc. 
         [0017]    In a first embodiment of the invention, congestion detection is based on UE measurements. UE measurements, however, with respect to interference generated by the system, are limited to I or . Therefore, to also account for I or , η UL  is obtained according to: 
         [0000]    
       
         
           
             
               
                 
                   
                     η 
                     UL 
                   
                   = 
                   
                     
                       ( 
                       
                         1 
                         + 
                         i 
                       
                       ) 
                     
                      
                     
                       
                         ∑ 
                         
                           i 
                           = 
                           1 
                         
                         N 
                       
                        
                       
                         1 
                         
                           1 
                           + 
                           
                             W 
                             
                               
                                 ρ 
                                 i 
                               
                                
                               
                                 R 
                                 i 
                               
                                
                               
                                 v 
                                 i 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     2 
                     ) 
                   
                 
               
             
           
         
       
     
         [0018]    where i is a predetermined value representing a ratio of I oc  to I or  and the sum represents I or . In the sum, N is the number of users in the cell; W is the carrier bandwidth; and ρ j , R j  and v j  are the signal-to-noise ratio (E b /N 0 ) bit rate, and activity factor of the j th  user, respectively. Multiplying I or  by (1+i) gives [I or +I or (i)] where I or (i)=I oc  thereby allowing both intra-cell and inter-cell interference to be accounted for in η UL . As may be seen from Equation 1, when η UL  tends to one, noise rise tends to infinity. 
         [0019]    Once η UL  is calculated, noise rise is obtained according to: 
         [0000]    
       
         
           
             
               
                 
                   
                     Noise_rise 
                     
                       d 
                        
                       
                           
                       
                        
                       B 
                     
                   
                   = 
                   
                     
                       - 
                       10 
                     
                     · 
                     
                       log 
                       [ 
                       
                         1 
                         - 
                         
                           
                             ( 
                             
                               1 
                               - 
                               
                                 
                                   α 
                                   UL 
                                 
                                 _ 
                               
                               + 
                               i 
                               + 
                               
                                 
                                   i 
                                    
                                   
                                       
                                   
                                    
                                   
                                     β 
                                     UL 
                                   
                                 
                                 _ 
                               
                             
                             ) 
                           
                            
                           
                             
                               ∑ 
                               
                                 j 
                                 = 
                                 1 
                               
                               N 
                             
                              
                             
                               1 
                               
                                 1 
                                 + 
                                 
                                   W 
                                   
                                     
                                       ρ 
                                       j 
                                     
                                      
                                     
                                       R 
                                       j 
                                     
                                      
                                     
                                       v 
                                       j 
                                     
                                   
                                 
                               
                             
                           
                         
                       
                       ] 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     3 
                     ) 
                   
                 
               
             
           
         
       
     
         [0020]    In  FIG. 1 , steps for monitoring congestion in the UL based on UE measurements in a CDMA system having MUD capabilities are shown and indicated generally with reference number  10 . 
         [0021]    The method begins with step  12  by calculating the UL load factor (η UL ) preferably using equation 2, as explained above. In step  14 , Equation 3 is preferably used to calculate the noise rise, as also explained above. The value of noise rise is proportional to congestion and is therefore evaluated in step  16  to determine whether congestion relieving measures should be implemented. If the value of noise rise is above a predetermined value, congestion relieving measures are implemented (step  18 ). The predetermined value of noise rise that is selected for triggering the congestion relieving measures may be any value. By way of example, in one embodiment, the predetermined value is between about 6 dB  and about 10 dB . 
         [0022]    If, in contrast, the value of noise rise is below the predetermined value, the method may start over at step  12 . The method may start over at step  12  at a predetermined time interval. The predetermined time interval may be any amount of time, as desired. By way of example, in one embodiment, the time interval is between about 3 seconds to about 5 seconds. 
         [0023]    In another embodiment of the invention, UL congestion detection may be based on RAN measurements. In this embodiment, both I oc  and I or  and both  α   UL  and  β   UL  may be defined by reading measurements available at the base station (BS). Therefore, in contrast to the first embodiment, η UL  and noise rise may be calculated without using a predetermined value to obtain I oc . 
         [0024]    More specifically, η UL  is obtained according to: 
         [0000]    
       
         
           
             
               
                 
                   
                     η 
                     UL 
                   
                   = 
                   
                     1 
                     - 
                     
                       noise_floor 
                       
                         total_perceived 
                          
                         _interference 
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     4 
                     ) 
                   
                 
               
             
           
         
       
     
         [0000]    where the noise floor is again all noise that is not related to the system and the total perceived interference comprises all non-cancelled interference at the receiver. Since the elements needed to calculate total perceived power are known, the total perceived power may be calculated according to (1−  α   UL )Ior+(1+  β   UL )I oc  thereby allowing η UL  to be calculated according to: 
         [0000]    
       
         
           
             
               
                 
                   
                     η 
                     UL 
                   
                   = 
                   
                     1 
                     - 
                     
                       noise_floor 
                       
                         
                           
                             ( 
                             
                               1 
                               + 
                               
                                 
                                   β 
                                   UL 
                                 
                                 _ 
                               
                             
                             ) 
                           
                            
                           Ioc 
                         
                         + 
                         
                           
                             ( 
                             
                               1 
                               - 
                               
                                 
                                   α 
                                   UL 
                                 
                                 _ 
                               
                             
                             ) 
                           
                            
                           Ior 
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     5 
                     ) 
                   
                 
               
             
           
         
       
     
         [0000]    Once η UL  is obtained, the effective noise rise is obtained according to: 
         [0000]    
       
         
           
             
               
                 
                   
                     Noise_rise 
                     
                       d 
                        
                       
                           
                       
                        
                       B 
                     
                   
                   = 
                   
                     10 
                     · 
                     
                       log 
                        
                       
                         [ 
                         
                           
                             
                               
                                 ( 
                                 
                                   1 
                                   + 
                                   
                                     
                                       β 
                                       UL 
                                     
                                     _ 
                                   
                                 
                                 ) 
                               
                                
                               Ioc 
                             
                             + 
                             
                               
                                 ( 
                                 
                                   1 
                                   - 
                                   
                                     
                                       α 
                                       UL 
                                     
                                     _ 
                                   
                                 
                                 ) 
                               
                                
                               Ior 
                             
                           
                           noise_floor 
                         
                         ] 
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     6 
                     ) 
                   
                 
               
             
           
         
       
     
         [0025]    In  FIG. 2 , steps for measuring and avoiding congestion in the UL based on RAN measurements in a CDMA system having MUD capabilities are shown and indicated generally with reference number  50 . 
         [0026]    The first step  52 , is to measure the noise floor. Then, in step  54 , to calculate η UL  preferably according to Equation 5, as explained above, where I oc , I or ,  α   UL  and  β   UL  are defined by reading measurements available at the BS. In an alternate embodiment, however, the ratio  α   UL  may be calculated according to: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       α 
                       _ 
                     
                     UL 
                   
                   ≅ 
                   
                     
                       
                         
                           ∑ 
                           
                             i 
                             = 
                             1 
                           
                           M 
                         
                          
                         
                           [ 
                           
                             1 
                             - 
                             
                               
                                 
                                   
                                     ( 
                                     
                                       
                                         
                                           Rx_code 
                                            
                                           
                                             _power 
                                             i 
                                           
                                         
                                         _ 
                                       
                                       · 
                                       
                                         SF 
                                         i 
                                       
                                     
                                     ) 
                                   
                                   / 
                                   
                                     
                                       SIR 
                                       _ 
                                     
                                     i 
                                   
                                 
                                 - 
                                 
                                   
                                     Ioc 
                                     i 
                                   
                                   _ 
                                 
                               
                               
                                 
                                   
                                     
                                       
                                         ( 
                                         
                                           
                                             
                                               total_perceived 
                                                
                                               _interference 
                                             
                                             _ 
                                           
                                           - 
                                           
                                             
                                               Ioc 
                                               i 
                                             
                                             _ 
                                           
                                         
                                         ) 
                                       
                                       - 
                                     
                                   
                                 
                                 
                                   
                                     
                                       
                                         Rx_code 
                                          
                                         
                                           _power 
                                           i 
                                         
                                       
                                       _ 
                                     
                                   
                                 
                               
                             
                           
                           ] 
                         
                       
                       M 
                     
                     . 
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     7 
                     ) 
                   
                 
               
             
           
         
       
     
         [0027]    In that embodiment,  β   UL  is considered negligible thereby eliminating the need for it to be read from the BS receiver. The additional parameters shown in Equation 7 are identified and defined from measurements taken at the BS receiver. By way of explanation, the additional parameters included in Equation 7 are Received Code Power for User i (Rx_Code_Power i ), Spreading Factor for User i (SF i ), and Number of Active Codes in the Timeslot (M). 
         [0028]    Once η UL  is obtained, noise rise is calculated according to Equation 6 in step  56 . As with the embodiment shown in  FIG. 1 , the value of noise rise is proportional to congestion. Therefore, the value of noise rise is evaluated in step  58  to determine whether congestion relieving measures should be implemented. If the value of noise rise is above a predetermined value, congestion relieving measures are implemented (step  60 ). Alternatively, if the value of noise rise is below the predetermined value, the method may start over at step  52  at a predetermined time interval. As with the embodiment described in conjunction with  FIG. 1 , the predetermined values of noise rise and time interval may be any values, as desired. 
         [0029]    The implementation of congestion relieving measures may be accomplished in a variety of ways. For example, the signal-to-noise ratio (E b /N 0 ) target of certain users may be reduced thereby forcing those users to reduce their transmission power. A drawback of this approach, however, is that those users will experience errors in the information transmitted and the quality of the link is greatly reduced. 
         [0030]    A preferred method for relieving congestion is to reduce the data transmission rate of a particular user or users. Users determine their transmission power depending on the data transmission rate, spreading factor gain and maximum transmission power and path loss. Therefore, reducing the data transmission rate of a particular user, which implicitly reduces power, allows the same signal-to-noise ratio to be achieved with the same spreading gain, but with less power. Furthermore, in WCDMA TDD systems, reducing the data transmission rate implies that a certain user is not transmitting at all in a timeslot thereby providing the additional benefit of relieving congestion for that timeslot. 
         [0031]    The preferred method for relieving congestion limits data transmission rate at the source; therefore no retransmissions are required. The selection of the user or users to whom the rates will be reduced is made by considering the transmitted power, received power and class of service. Those factors are considered for each user and may be considered individually, collectively or as a particular combination thereof, as desired. The user or users that contribute the most to the interference and have the lowest service class priority are preferably chosen as candidates for data rate reduction. 
         [0032]    The preferred method for relieving congestion is shown in  FIG. 3  and indicated generally with reference numeral  100 . To begin, transmission power, received power and class of service are determined for each user in steps  102 ,  104  and  106 , respectively. Then, in step  108 , each user&#39;s contribution to noise rise is calculated. As explained, noise rise may be calculated according to Equation 3 or Equation 6, as desired. 
         [0033]    In step  110 , the user that collectively contributes the most to the noise rise and has the lowest service priority is selected. To determine the selected user, a predetermined weighting factor may be used for each parameter. It is important to note that any value may be used for the weighting factor so that the influence of priority and noise contribution in selecting a user may be adjusted as desired. Furthermore it may be desirable to use only one of those parameters or, alternatively, it may be desirable to use additional parameters which, like noise contribution and priority, may be weighted as desired. The criteria for selecting a user is completely flexible and may be any criteria which accurately identifies users having data transmission rates that may be reduced so as to reduce congestion. Therefore, the selected user may, for example, be determined according to: 
         [0000]      User_selected= W 1(priority)+ W 2(noise contribution)  Equation 8
 
         [0034]    In step  112 , the data transmission rate of the selected user is reduced. In step  113 , the amount of congestion is evaluated to determine whether congestion has been relieved. If the corresponding reduction in the noise rise is sufficient to reduce the value of noise rise below the predetermined value at which congestion is detected, the method ends and congestion monitoring, as described in conjunction with  FIGS. 1 and 2 , may continue (step  114 ). Alternatively, if the congestion has not been relieved so that the value of noise rise is below the predetermined value, congestion still exists and the method  100  returns to step  110  or  102 , as desired, and continues until the congestion is relieved. 
         [0035]    Referring now to  FIG. 4 , a system  200  is shown for controlling congestion in the UL based on UE measurements. In system  200 , congestion in the UL is monitored and controlled using UE measurements. The system  200  comprises at least one UE  202 , a BS or node-B  214  and a radio network controller  210 . 
         [0036]    The UE comprises a receiver  203  having MUD capabilities, an I or  measuring device  204  and an I or  signaling device  206 . The I or  measuring device  204  utilizes information available at the UE  202  to measure the amount of interference generated by the system within the cell in which the UE  202  is currently located. As previously explained, that type of interference is referred to as intra-cell interference (I or ). 
         [0037]    The BS or node-B  214  includes a receiver  205  having a MUD and an I or  signal receiver  208 . The I or  measured by measuring device  204  is transmitted from the I or  signaling device  206  of the UE  202  to the I or  signal receiver  208  of the BS or node-B  214 . The BS or node-B  214  communicates the I or  to a radio network controller (RNC)  210  comprising a radio resource management (RRM) device  212 . The RRM  212 , in conjunction with the BS or node-B  214 , if needed, processes I or  so that the total interference, as affected by the MUD(s)  203 ,  205 , may be obtained. As explained above, the total interference may be obtained using I or ,  α   UL ,  β   UL  and i. 
         [0038]    Once the total interference is obtained, η UL  and noise rise is also obtained. If the noise rise is above a predetermined value, each users&#39; contribution to the noise rise is measured. Preferably, each users&#39; transmission power, received power and class of service are also measured. The data transmission rate of the user currently having the highest contribution to noise rise and the lowest class of service is reduced as needed until the overall noise rise falls below the predetermined value. In other words, if reducing the data transmission rate of what was the highest contributor to noise rise is not sufficient to reduce noise rise to below the predetermined value, the method continues by recalculating each users&#39; noise rise contribution and reducing the data transmission rate of the highest contributor. Alternatively, the method may continue by using the current user calculations and simply reduce the rate of the next highest contributor. 
         [0039]    In  FIG. 5 , another embodiment of a system for controlling congestion in the UL is shown and indicated generally with reference numeral  300 . In system  300 , congestion in the UL is monitored and controlled using RAN measurements. The system  300  comprises at least one UE  301 , a BS or node-B  306  and a RNC  308 . 
         [0040]    The UE  301  comprises a receiver  303  having MUD capabilities. The BS or node-B  306  includes a receiver  305  having MUD capabilities, an I or  measuring device  302  and an I oc  measuring device  304 . The BS or node-B  306  communicates the I or  and I oc  to a radio network controller (RNC)  308  comprising a radio resource management (RRM) device  310 . The RRM  310 , in conjunction with the BS or node-B  306 , if needed, processes I or  and I oc  so that the total interference, as affected by the MUD(s)  303 ,  305 , may be obtained. As explained above, the total interference may be obtained using I or , I oc ,  α   UL , and  β   UL . 
         [0041]    Once the total interference is obtained, η UL  and noise rise is also obtained. If the noise rise is above a predetermined value, each users&#39; contribution to the noise rise is measured. Preferably, each users&#39; transmission power, received power and class of service is also measured. The data transmission rate of the user currently having the highest contribution to noise rise and the lowest class of service is reduced as needed until the overall noise rise falls below the predetermined value, as explained in connection with  FIG. 4 . 
         [0042]    Although the present invention has been described in detail, it is to be understood that the invention is not limited thereto, and that various changes may be made therein without departing from the spirit and scope of the invention, which is defined by the attached claims.