Method and Arrangement for DL-OTDOA (Downlink Observed Time Difference of Arrival) Positioning in a LTE (Long Term Evolution) Wireless Communications System

Abstract

The present invention relates generally to methods and arrangements for positioning in a wireless communications system. In particular, the present invention relates to improving positioning accuracy. The invention provides methods and arrangements for scheduling positioning subframes for allowing aligning of positioning subframes across a number of cells in order to reduce the interference from data symbols of cells in the neighborhood of a cell serving the UE that is performing positioning measurements. A time instance during which transmission of the positioning subframes is to occur in a wireless communications network is selected. The base stations in the wireless communications network are informed about the selected time instance, whereupon the base stations schedule and transmit the positioning subframes based on the selected time instance, whereby the positioning subframes are aligned throughout the network.

1 . A method in a network node for scheduling the transmission of positioning subframes from different base stations in a wireless communications network, the method comprising:
 selecting a time period during which transmission of positioning subframes is to occur from one or more of the different base stations; and   informing one or more of the base stations that positioning subframes are to be transmitted during the selected time period to thereby align the positioning subframes across the different base stations.   
     
     
         2 . The method according to  claim 1 , wherein normal subframes in the wireless communication network each include a region in which data is scheduled, and wherein no data is scheduled in at least a portion of a corresponding region of positioning subframes in the wireless communication network. 
     
     
         3 . The method according to  claim 1 , wherein the positioning subframes are Multicast Broadcast Multimedia Single Frequency Network subframes. 
     
     
         4 . The method according to  claim 1 , wherein the selected time period is associated with a system frame number. 
     
     
         5 . The method according to  claim 1 , further comprising:
 retrieving system time information obtained from a global system clock or a Global Positioning System receiver; and   informing the one or more base stations of the system time information.   
     
     
         6 . The method according to  claim 1 , wherein the network node is a positioning node. 
     
     
         7 . The method according to  claim 1 , wherein the network node is an evolved Serving Mobile Location Center. 
     
     
         8 . The method according to  claim 1 , wherein the network node is one of the different base stations. 
     
     
         9 . The method according to  claim 8 , further comprising:
 scheduling the transmission of a positioning subframe from the network node based on at least the selected time period; and   transmitting the scheduled positioning subframe.   
     
     
         10 . The method according to  claim 9 , wherein said scheduling comprises scheduling the transmission of a positioning subframe to occur during a time period which deviates from the selected time period by less than half the length of a subframe. 
     
     
         11 . The method according to  claim 9 , further comprising scheduling transmission of the positioning subframe from the network node also based on system time information. 
     
     
         12 . The method according to  claim 8 , further comprising:
 receiving information from another one of the base stations indicating that transmission of a positioning subframe from that base station is scheduled to occur during a time period that is different from the selected time period; and   adjusting the selected time period according to the time period indicated by the received information.   
     
     
         13 . The method according to  claim 12 , further comprising informing one or more of the different base stations that transmission of positioning subframes is to occur during the time period indicated by the received information. 
     
     
         14 . The method according to  claim 12 , wherein said receiving comprises receiving the information over an X2 interface. 
     
     
         15 . A method in a base station of a wireless communications network for scheduling the transmission of a positioning subframe from that base station, the method comprising:
 receiving from a network node information indicating a time period during which the transmission of positioning subframes is to occur from one or more different base stations in the network;   scheduling the transmission of a positioning subframe from said base station based on the time period indicated by the received information to thereby align the positioning subframes across the different base stations; and   transmitting the scheduled positioning subframe.   
     
     
         16 . The method according to  claim 15 , wherein normal subframes in the wireless communication network each include a region in which data is scheduled, and wherein no data is scheduled in at least a portion of a corresponding region of positioning subframes in the wireless communication network. 
     
     
         17 . The method according to  claim 15 , wherein the positioning subframes are Multicast Broadcast Multimedia Single Frequency Network subframes. 
     
     
         18 . The method according to  claim 15 , wherein the time period indicated by the received information is associated with a system frame number. 
     
     
         19 . The method according to  claim 15 , wherein said scheduling comprises scheduling the transmission of a positioning subframe to occur during a time period which deviates from the selected time period by less than half the length of a subframe. 
     
     
         20 . The method according to  claim 15 , further comprising:
 receiving system time information obtained from a global system clock or a Global Positioning System receiver; and   scheduling the transmission of the positioning subframe from said base station also based on said system time information.   
     
     
         21 . The method according to  claim 15 , wherein said network node is a positioning node. 
     
     
         22 . The method according to  claim 15 , wherein said network node is an evolved Serving Mobile Location Center. 
     
     
         23 . The method according to  claim 15 , further comprising informing one or more of the different base stations that transmission of positioning subframes is to occur during the time period indicated by the received information. 
     
     
         24 . The method according to  claim 23 , wherein the network node is a base station and said informing is performed over an X2 interface. 
     
     
         25 . The method according to  claim 24 , wherein the network node is a base station.