Methods and arrangements in a radio communications system

Abstract

Methods and an arrangement for synchronizing communication of framed data via asynchronous base stations (BS 1, BS 2 ) in a cellular communication system are presented. The synchronization methods are performed continuously by sending out certain system frame counter states from a central node in the system to all its connected base stations (BS 1, BS 2 ). Each base station (BS 1, BS 2 ) includes a local frame counter (LFC BS1 , LFC BS2 ), which generates local frame counter states (t 1 ( 1 )-t 1 ( 4 ), t 2 ( 1 )-t 2 ( 4 )) correlated to the system frame counter states. Transmission of information via the base stations (BS 1, BS 2 ) is synchronized by assigning each data frame (DR( 1 )-DR( 4 )) a particular frame number, which is given by the local frame counter states (t 1 ( 1 )-t 1 ( 4 ), t 2 ( 1 )-t 2 ( 4 )), so that data framed (DF( 1 )-DF ( 4 )) having identical numbers contain copies of a certain data packet. Correct frame numbers are derived from common downlink channel offset measurements (CCO 1, CCO 2 ) carried out in the base stations (BS 1, BS 2 ), and timing advances values (TA 2 ) and downlink channel offsets (DCO 1, DCO 2 ) calculated in the central node.

1. A method in a cellular radio communications system, which is arranged for communicating information in data frames (DF) of a predetermined duration (T ƒ ) the system comprising at least one central node (RNC 1 , RNC 2 ) and at least one asynchronous base station (BS 1 -BS 5 ), for synchronizing all base stations (BS 1 , BS 2 ) that are connected to one (RNC 1 ) of the at least one central node (RNC 1 , RNC 2 ) independently of any global time reference for the system, the method comprising the steps of:
 sending a system frame counter state (SFC) from the central node (RNC 1 ) to all its connected base stations (BS 1 , BS 2 ), the frame counter state being incremented one step for each of the data frames (DF); and  
 aligning in each of the connected base stations (BS 1 , BS 2 ) a state of a respective local frame counter (LFC BS1 , LFC BS2 ) with the system frame counter state (SFC);  
 wherein each of the data frames (DF) is associated with a specific frame number (t 1 ( 1 )-t 1 ( 4 ), t 2 ( 1 )-t 2 ( 4 )) which is derived from the responsive local frame counter (LFC BS1 , LFC BS2 ).  
 
     
     
       2. The method according to  claim 1 , wherein the system frame counter state (SFC) is incremented one step after each lapse of one of the data frames (DF) and wherein each of the base stations (BS 1 -BS 5 ) has at its disposal at least one common downlink control channel (CDCH 1 , CDCH 2 ), the method further comprising the steps of:
 in each of the connected base stations (BS 1 , BS 2 ), measuring a common downlink control channel offset value (CCO 1 , CCO 2 ) between the local frame counter states (LFC BS1 , LFC BS2 ) and a corresponding common downlink control channel (CDCH 1 , CDCH 2 ), where the local frame counter state (LFC BS1 , LFC BS2 ) is incremented at a rate correlated to the system frame counter (SFC) step rate; and  
 reporting the common downlink control channel offset values (CCO 1 , CCO 2 ) to the central node (RNC 1 ).  
 
     
     
       3. The method according to  claim 1 , wherein an update of the system frame counter state (SFC) is sent out at regular time intervals (T). 
     
     
       4. The method according to  claim 1 , wherein a one-way delay (D 1 , D 2 ) is determined for each connection between the central node (RNC 1 ) and all its connected base stations (BS 1 , BS 2 ), and that the one-way delay (D 1 , D 2 ) is compensated for. 
     
     
       5. The method according to  claim 4 , wherein the one-way delay (D 1 , D 2 ) is calculated through a procedure comprising the consecutive steps of:
 sending a round-trip-delay message (RTD 1 ) back and forth between the central node (RNC 1 ) and a given base station (BS 1 );  
 calculating a difference between an arrival time (t α ) and a corresponding sending time (t s ) of the round-trip-delay message (RTD 1 ) and dividing the calculated difference by two;  
 repeating the steps of sending the round-trip-delay message (RTD 1 ) and calculating the difference a predetermined number of times to produce (p) differences; and  
 averaging over the (p) differences.  
 
     
     
       6. The method according to  claim 5 , wherein the round-trip-delay message (RTD 1 ) is originated from a base station (BS 1 , BS 2 ). 
     
     
       7. The method according to  claim 6 , wherein the one-way delay (D 1 , D 2 ) is compensated for in each of the connected base stations (BS 1 , BS 2 ) by adjusting the local frame counter state according to the equation:
   LFC BSx =SFC+D x    
 
       where
 LFC BSx  denotes a respective one of the local frame counter states LFC BS1 , and LFC BS2 , whose resolution is a fraction of a step  
 SFC denotes the system frame counter state; and  
 D x  denotes the one-way delay D 1  or D 2 .  
 
     
     
       8. The method according to  claim 5 , wherein the round-trip-delay message (RTD 1 ) originates from the central node (RNC 1 ). 
     
     
       9. The method according to  claim 8 , wherein the one-way delay (D 1 , D 2 ) is compensated for in the central node (RNC 1 ) by bringing forward in time the transmission of each system frame counter state (SFC x ) message to the connected base stations (BS 1 , BS 2 ) according to the equation:
   SFC x =SFC−D x    
 
       where
 SFC x  denotes a system frame counter message sent to a particular base station (X=1: BS 1 , X=2: BS 2 ),  
 SFC denotes the system frame counter state and  
 D x  denotes the one-way delay D 1  or D 2 .  
 
     
     
       10. The method according to  claim 1 , wherein the at least one central node (RNC 1 , RNC 2 ) is a radio network control node. 
     
     
       11. The method according to  claim 2 , wherein the at least one common downlink control channel (CDCH 1 , CDCH 2 ), downlink channels (DCH 1 , DCH 2 ) and uplink channel(s) (UCH 2 ) are distinguished from each other through either
 (A) a code division of a radio spectrum,  
 (B) a code and frequency division of the radio spectrum,  
 (C) a code and time division of the radio spectrum, or  
 (D) a combination of code, frequency and time division of the radio spectrum.  
 
     
     
       12. A method in a cellular radio communications system comprising at least one central node (RNC 1 , RNC 2 ), which is connected to at least one asynchronous base station (BS 1 -BS 5 ), each of which serves at least one geographical sector (s 11 -s 56 ), which in turn are each associated with a common downlink control channel (CDCH 1 , CDCH 2 ),
 where the base stations (BS 1 -BS 5 ) communicate information with mobile stations (MS 1 -MS 4 ), the information being divided into data packets (DP), which are transmitted in data frames (DF) 
 on downlink channels (DCH 1 , DCH 2 ) via one or more sectors (s 23 , s 24 ) to the mobile stations (MS 1 -MS 4 ), and  
 on uplink channels (UCH 2 ) from the mobile stations (MS 1 -MS 4 ) via one or more sectors (s 23 , s 24 ),  
 
 for establishing a connection between one of the mobile stations (MS 2 ) and at least one base station (BS 1 ), the method comprising the steps of:  
 sending a system frame counter state (SFC) from one central node (RNC 1 ) of the at least one central node (RNC 1 , RNC 2 ) to all its connected base stations (BS 1 , BS 2 ), the frame counter state being incremented one step for each of the data frames (DF) and being incremented one step after each lapse of one of the data frames (DF);  
 aligning in each of the connected base stations (BS 1 , BS 2 ) a state of a respective local frame counter (LFC BS1 -LFC BS2 ) with the system frame counter state (SFC), each of the data frames (DF) being associated with a specific frame number (t 1 ( 1 )-t 1 ( 4 ), t 2 ( 1 )-t 2 ( 4 )) which is derived from the respective local frame counter (LFC BS1 -LFC BS2 );  
 in each of the connected base stations (BS 1 , BS 2 ), measuring a common downlink control channel offset value (CCO 1 , CCO 2 ) between the local frame counter states (LFC BS1 -LFC BS2 ) and a corresponding common downlink control channel (CDCH 1 , CDCH 2 ), where the local frame counter state (LFC BS1 -LFC BS2 ) is incremented at a rate correlated to the system frame counter (SFC) step rate;  
 reporting the common downlink control channel offset values (CCO 1 , CCO 2 ) to the at least one central node (RNC 1 , RNC 2 );  
 defining for the mobile station (MS 2 ) an active set (AS) in which at least one of the downlink channels (DCH 1 ) and one of the uplink channels (UCH 2 ) is specified;  
 for each of the at least one downlink channels (DCH 1 ) in the active set (AS), setting a timing advance value (TA 1 ), which indicates an offset between the common downlink control channel (CDCH 1 ) and the downlink channel (DCH 1 );  
 for each of the at least one downlink channels (DCH 1 ) in the active set (AS), calculating a downlink channel offset (DCO 1 ) as a sum (CCO 1 +TA 1 ) of a common downlink control channel offset (CCO 1 ) and the timing advance value (TA 1 );  
 assigning a specific frame number (t 1 ( 1 )-t 1 ( 4 )) to each data frame (DF( 1 )-DF( 4 )) on each of the at least one downlink channels (DCH 1 ), by giving an initial data frame (DF( 1 )) a first number (t 1 ( 1 )) and each following data frame (DF( 2 )-DF( 4 )) an integer incrementation (t 1 ( 2 ), t 1 ( 3 ), t 1 ( 4 )) of this number (t 1 ( 1 )) equal to an order of each responsive data frame (DF( 2 )-DF( 4 )) in relation to the initial data frame (DF( 1 )).  
 
     
     
       13. The method according to  claim 12 , wherein during downlink communication of information, data packets (DP) are buffered (B) in each of the connected base stations (BS 1 , BS 2 ) until the frame number for the data frames transmitting each specific data packet (DP( 1 )-DP( 4 )) matches the frame number (t 1 ( 1 )-t 1 ( 4 ), t 2 ( 1 )-t 2 ( 4 )) on the respective downlink channel (DCH 1 , DCH 2 ). 
     
     
       14. The method according to  claim 13 , wherein the buffering (B) holds data packets (DP) up to a maximum number and that a data packet (DP) is discarded if it arrives at one of the connected base stations (BS 1 , BS 2 ) too late to meet the frame number on the respective downlink channel (DCH 1 ; DCH 2 ) indicated by the central node (RNC 1 ). 
     
     
       15. The method according to  claim 12 , wherein during uplink communication of information, data packets (DP) are received in the connected base stations (BS 1 , BS 2 ) in data frames (DF), being numbered (t 1 ( 1 )-t 1 ( 4 ), t 2 ( 1 )-t 2 ( 4 )) in relation to the frame numbering of the downlink channels (DCH 1 , DCH 2 ) indicated by the central node (RNC 1 ) and that a diversity procedure is performed in the central node (RNC 1 ) on data packets (DP), which are sent in data frames (DF) having identical numbers. 
     
     
       16. The method according to  claim 15 , wherein the diversity procedure is performed when all copies of a given data packet (DP) have arrived at the central node (RNC 1 ), but no later than a time (τ) after arrival of a first copy of the data packet (DP). 
     
     
       17. The method according to  claim 16 , wherein, in the diversity procedure, one data packet (DP) having a highest quality is selected to represent the communication of information. 
     
     
       18. The method according to  claim 16 , wherein, in the diversity procedure, contents of all data packets (DP) are combined to form a representation of the communication of information. 
     
     
       19. A method in a cellular radio communications system comprising at least one central node (RNC 1 , RNC 2 ), which is connected to at least one asynchronous base station (BS 1 -BS 5 ), each of which serves at least one geographical sector (s 11 -s 56 ), which in turn are each associated with a common downlink control channel (CDCH 1 , CDCH 2 ),
 where the base stations (BS 1 -BS 5 ) communication information with mobile stations (MS 1 -MS 4 ), the information being divided into data packets (DP), which are transmitted in data frames (DF) 
 on downlink channels (DCH 1 , DCH 2 ) via one or more sectors (s 23 , s 24 ) to the mobile stations (MS 1 -MS 4 ), and  
 on uplink channels (UCH 2 ) from the mobile stations (MS 1 -MS 4 ) via one or more sectors (s 23 , s 24 ),  
 
 for commencing communication via at least one second sector (s 21 ) with one of the mobile stations (MS 2 ) which is already communicating information via at least one first sector (s 14 ) specified in an active set (AS) for the mobile station (MS 2 ), the method comprising the steps of:  
 sending a system frame counter state (SFC) from one central node (RNC 1 ) of the at least one central node (RNC 1 , RNC 2 ) to all its connected base stations (BS 1 , BS 2 ), the frame counter state being incremented one step for each of the data frames (DF) and being incremented one step after each lapse of one of the data frames (DF);  
 aligning in each of the connected base stations (BS 1 , BS 2 ) a state of a respective local frame counter (LFC BS1 -LFC BS2 ) with the system frame counter state (SFC), each of the data frames (DF) being associated with a specific frame number (t 1 ( 1 )-t 1 ( 4 ), t 2 ( 1 )-t 2 ( 4 )) which is derived from the respective local frame counter (LFC BS1 -LFC BS2 );  
 in each of the connected base stations (BS 1 , BS 2 ), measuring a common downlink control channel offset value (CCO 1 , CCO 2 ) between the local frame counter states (LFC BS1 -LFC BS2 ) and a corresponding common downlink control channel (CDCH 1 , CDCH 2 ), where the local frame counter state (LFC BS1 -LFC BS2 ) is incremented at a rate correlated to the system frame counter (SFC) step rate;  
 reporting the common downlink control channel offset values (CCO 1 , CCO 2 ) to the at least one central node (RNC 1 , RNC 2 );  
 measuring at least one frame offset value (O ƒ12 ) between a downlink channel (DCH 1 ) in the active set (AS) and a second common downlink control channel (CDCH 2 ), associated with the second sector (s 21 ), not included in the active set (AS),  
 reporting the frame offset value (O ƒ12 ) to a central node (RNC 1 ),  
 updating the active set (AS) by adding thereto the second sector (s 21 ),  
 calculating a timing advance value (TA 2 ) and a downlink channel offset value (DCO 2 ) for at least one second downlink channel (DCH 2 ) in the second sector (s 21 ),  
 setting an offset between data frames (DFs) transmitted on the at least one second downlink channel (DCH 2 ) and the second common downlink control channel (CDCH 2 ) equal to the timing advance value (TA 2 ),  
 assigning a specific frame number (t 2 ( 1 )-t 2 ( 4 )) to each data frame (DF( 1 )-DF( 4 )) on the second downlink channels (DCH 2 ), by giving an initial data frame (DF ( 1 )) after a current local frame counter state from the second series of local frame counter states (LFC BS2 (n)) a frame number (t 2 ( 1 )) equal to a following local frame counter state from this series and each subsequent data frame (DF( 2 )-DF( 4 )) an integer incrementation (t 2 ( 2 ) −t 2 ( 4 )) of this frame number (t 2 ( 1 )) equal to the order of each responsive data frame (DF( 2 )-DF( 4 )) in relation to the initial data frame (DF( 1 )).  
 
     
     
       20. The method according to  claim 19 , wherein the step of calculating is carried out according to the equation:
   TA 2 =T ƒ −O ƒ12    
 
       where
 TA 2  denotes the timing advance value,  
 T ƒ  denotes the duration of a data frame (DF), and  
 O ƒ12  denotes the frame offset value;  
 
       and
   DCO 2 =CCO 2 +TA 2 +i·T ƒ   
 
       where
 DCO 2  denotes a downlink channel offset for the at least one second downlink channel (DCH 2 ) representing how data frames (DF) of the at least one second downlink channel (DCH 2 ) are numbered (t 2 ( 1 )-t 2 ( 4 )) relative to the local frame counter states (LFC BS2 (n)) in the second sector (s 21 ),  
 CCO 2  denotes the common downlink control channel offset value between the second series of local frame counter states (LFC BS2 (n)) and the common downlink control channel (CDCH 2 ),  
 TA 2  denotes the timing advance value, is an integer, which is set to a value that minimizes the modulus of the difference (|DCO 1 −DCO 21 | min ), between the frame number (t 1 ) given by the first downlink channel offset (DCO 1 ) and the frame number (t 2 ) given by the second downlink channel offset (DCO 2 ), and  
 T ƒ  denotes the duration of a data frame (DF).  
 
     
     
       21. The method according to  claim 20 , wherein the downlink channel offset (DCO 1 ) for the first downlink channel (DCH 1 ) is re-calculated according to the equation:
   DCO 1 =CCO 1 +TA 1   
 
       where
 CCO 1  is the latest common downlink control channel offset value between the first series of local frame counter states (LFC BS1  (n)) and the first common downlink control channel (CDCH 1 ) reported from the first base station (BS 1 ) to the central node (RNC 1 ),  
 TA 1  is equal to the timing advance value for the first downlink channel (DCH 1 ).  
 
     
     
       22. An arrangement for communicating framed information in a cellular radio communications system comprising at least one central node (RNC 1 ), which is connected to at least one asynchronous base station (BS 1 , BS 2 ) through which data packets (DPs) are communicated on downlink channels (DCH 1 , DCH 2 ) and uplink channels (UCH 1 , UCH 2 ) with mobile stations (MS 2 ) and where control signals are transmitted on common downlink control channels (CDCH 1 , CDCH 2 ) to the mobile stations (MS 2 ), wherein the at least one central node (RNCL) comprises a master timing unit for generating system frame counter states (SFC) to be sent to the at least one base station (BS 1 , BS 2 ), a master control unit for calculating timing advance values (TA) and downlink channel offset values (DCO 1 , DCO 2 ) to be used while communicating data packets (DPs) in numbered data frames (DF) on the downlink channels DCH 1 , DCH 2 ), a diversity handover unit for executing simultaneous communication via more than one of the at least one base station (BS 1 , BS 2 ) with a particular mobile station (MS 2 ). 
     
     
       23. The arrangement according to  claim 22 , wherein the at least one central node (RNC 1 ) further comprises a clock generator for synchronizing all other units included in the at least one central node (RNC 1 ), a reference time generator providing an absolute time reference (T R ) to be used by the master timing unit and a switching unit for alternately connecting the diversity handover unit to one specific base station of the at least one base station (BS 1 , BS 2 ). 
     
     
       24. The arrangement according to  claim 23 , wherein the reference time generator is a GPS receiver. 
     
     
       25. The arrangement according to  claim 22 , wherein each of the base stations (BS 1 , BS 2 ) comprises:
 a clock generator for synchronizing all other units in the base station (BS 1 , BS 2 );  
 a timing unit for receiving the system frame counter states (SFC) and generating local frame counter states (LFC BS1 , LFC BS2 );  
 a transceiver unit for communicating data packets (DPs) in numbered data frames (DF) and for measuring offset values (CCO 1 , CCO 2 ) between the local frame counter states (LFC BS1 , LFC BS2 ) and the common downlink control channels (CDCH 1 , CDCH 2 ); and  
 a timing control unit for receiving the timing advance values (TA 1 , TA 2 ) and the downlink channel offset values (DCO 1 , DCO 2 ) and for controlling (I 1 , I 2 ) the transceiver unit.  
 
     
     
       26. The arrangement according to  claim 22 , wherein at least one particular and one separate connection is dedicated for transmitting the system frame counter states (SFC) from the at least one central node (RNC 1 ) to each of the base stations (BS 1 , BS 2 ). 
     
     
       27. The arrangement according to  claim 26 , wherein each of the particular and separate connections is compensated for a one-way delay D 1 , D 2 ) between the at least one central node (RNC 1 ) and each respective base station (BS 1 , BS 2 ). 
     
     
       28. The arrangement according to  claim 25 , wherein each of the base stations (BS 1 , BS 2 ) further comprises a first buffer unit for buffering data packets (DPs) which have been transmitted from the at least one central node (RNC 1 ). 
     
     
       29. The arrangement according to  claim 28 , wherein an output of the first buffer unit is connected to the transceiver unit. 
     
     
       30. The arrangement according to  claim 22 , wherein the at least one central node (RNC 1 ) further comprises a second buffer unit for buffering data packets (DPs), which have been transmitted from the base stations (BS 1 , BS 2 ). 
     
     
       31. The arrangement according to  claim 30 , wherein an output of the second buffer unit is connected to the diversity handover unit. 
     
     
       32. The arrangement according to  claim 22 , herein each base station includes a timing unit to receive the system frame counter states (SFC) and to create local frame counter states (LFC BS1 , LFC BS2 ), the system frame counter states (SFC) being incremented one step for each data frame (DF) and where each of said data frames (DF) being associated with a specific frame number (t 1 ( 1 )-t 1 ( 4 ), t 2 ( 1 )- 2 ( 4 )) is derived from a respective local frame counter (LFC BS1 , LFC BS2 ). 
     
     
       33. A method to attain simultaneous transmission in a cellular radio communication system comprising a central node, a first and a second asynchronous base station said base stations being connected to said central node, and a mobile station which is communicating information in data frames of a predetermined duration with said first base station, said second base station to be added for communication in soft handover, the method comprising:
 a) the mobile station measuring and reporting to said central node a frame offset value between the mobile's current downlink channel  current downlink channel of the mobile station and a second  common downlink control channel,  
 b) said central node, based on this information, calculating a timing advance value needed in a target cell between a dedicated channel frame structure and a common control channel frame structure, and informing the second base station of this, thus providing aligned transmission timings between a dedicated channel frame structure in a target cell  the dedicated channel frame structure in a target cell and a home cell,  
 c) maintaining a local frame counter state per dedicated channel connection,  
 d) initializing the local frame counter for the dedicated channel in the target cell such that a frame of the target cell frame structure is assigned the same dedicated channel data frame number as the corresponding aligned frame of the home cell, and  
 e) numbering the data frames to be transmitted on the dedicated channel of the target cell and the home cell, such that the data frame with identical data frame number is sent to both the first and the second base station from said central node, each base station, whereby a base station can start transmission  each of said first and second base stations can start transmission of data frames from the first dedicated data channel  target cell dedicated channel with a certain frame number with the same number, on the second dedicated data channel with the same number  a home cell dedicated channel.  
 
     
     
       34. Method  The method according to  claim 33 , further comprising:
 measuring a  the frame offset value between said first  current downlink channel of the mobile station and the second  common downlink control channel, and, based on the measuring,  
 calculating a second  timing advance value for said  a second downlink channel,  
 setting a second downlink channel offset value for the second downlink channel added to said second  timing advance value for said second downlink channel, and  
 minimizing the difference of the first and second downlink channel offset values, thereby granting that a current data frame number of the first downlink channel is aligned with a corresponding data frame number of said second downlink channel.  
 
     
     
       35. Method  The method according to  claim 34 , wherein:
 said second downlink offset value is calculated according to the sum of the second common downlink control channel offset value, the timing advance value of the second downlink channel and a multiple of the frame time, and that the multiple is chosen so that it minimizes the difference between the first and second downlink channel offsets according to step b).  
 
     
     
       36. Method  The method according to  claim 34 , wherein:
 said measuring according to step a) is done by the mobile station upon instruction from said radio  central node.  
 
     
     
       37. Method  The method according to  claim 34 , wherein:
 said second common downlink control channel offset value is reported to said control  central node which is calculating said second  timing advance value for said second downlink channel according to step c).  
 
     
     
       38. Method  The method according to  claim 37 , wherein the second common downlink control channel offset value between the respective common downlink control channel and the local frame counter state in the respective base station which offset value is reported regularly by the respective first and second base station to said control  central node. 
     
     
       39. Arrangement  An arrangement for communicating framed information in a cellular radio communication system comprising at least one central node which is connected to at least two asynchronous base stations through which data packets are communicated on dedicated downlink channels and uplink channels with mobile stations, comprising
 a diversity handover unit for executing simultaneous communication via more than one base station with a particular mobile station,  one of said mobile stations, 
 a master control unit for calculating timing advance values in order to align transmission timing between frame structures of the dedicated downlink channels and uplink channels in the at least two asynchronous base stations, wherein  
 each base station includes: 
 a local frame counter to givemeans to generate a local frame counter state per dedicated channel connection,  
 means to transmit a numbered data packet received from the central node in a dedicated channel frame with a corresponding data frame counter number, and 
 
 each central node includes: 
 a data packet counter state per mobile station connection for assigning identical numbers to all data packets containing equivalent data, that is sent to the at least two asynchronous base stations involved in the connection with the mobile station.  
 
 
     
     
       40. The arrangement according to  claim 39 , wherein each base station further includes:
 at least one common local frame counter not individually associated with any specific dedicated channel which is used as a reference for initializing the local frame counter state at establishment of one of the dedicated downlink channels in the base station,  
 a timing control unit, receiving downlink channel offset information from the central node, and  
 means to initialize the local frame counter state at establishment of a dedicated downlink channel,  each of said dedicated downlink channels by applying the offset information relative to the local frame counter state.