Patent EP-2525236-A1 (EP)
Inventor: HACH RAINER
IPC: G01S5/02
Filed: 2011-09-16
Abstract: A method for determining an instantaneous phase difference            C   ^         A   1     ⁢     A   2           t            between time bases of at least two location anchors (A1, A2) for a desired point in time (t), each of the location anchors having transmitting and receiving access to a joint broadcast transmission medium and a respective time base for measuring time, the method comprising: 
- a first of the location anchors (A1 ) broadcasting a first broadcast message at least twice, that is, at different times; 
- the first location anchor and at least a second of the location anchors (A2, An) receiving the first broadcast messages; 
- the second location anchor (A2, An) broadcasting a second broadcast message at least twice, that is, at different times; 
- the second location anchor and at least the first location anchor receiving the second broadcast messages; 
- the first (A1) and the second location anchors (A2, An) each generating time-of-arrival stamps, hereinafter TOA stamps, which are indicative of respective first and second times of reception                TOA       A   1     ,     A   1     ,   t   =     t   1         ,         TOA       A   1     ,     A   2     ,   t   =     t   1         ,         TOA       A   2     ,     A   1     ,   t   =     t   2         ,         TOA       A   2     ,     A   2     ,   t   =     t   2                      of the first and second broadcast messages in terms of their respective time base, wherein the first and second location anchor not only generate TOA stamps                TOA       A   1     ,     A   2     ,   t   =     t   1         ,         TOA       A   2     ,     A   1     ,   t   =     t   2                      for the broadcast messages received from the respective other of the first and second location anchors, but also TOA stamps        (       TOA       A   1     ,     A   1     ,   t   =     t   1         ,                 TOA       A   2     ,     A   2     ,   t   =     t   2         )          for the broadcast messages received from the respective same location anchor (A1, A2) itself; 
- the first and second location anchor providing the generated TOA stamps to a location server in a manner that allows the location server an identification of also the location anchor broadcasting the broadcast message subject to a respective TOA stamp, of the location anchor receiving the broadcast message subject to a respective TOA stamp, and of the broadcast message; 
- the location server calculating time-difference-of-arrival values, hereinafter TDOA values                TDOA       A   1     ,     A   1     ,     A   2     ,   t   =     t   1         ,         TDOA       A   2     ,     A   1     ,     A   2     ,   t   =     t   2                 ,        from each pair of collected TOA stamps                TOA       A   1     ,     A   1     ,   t   =     t   1         ,         TOA       A   1     ,     A   2     ,   t   =     t   1         ;         TOA       A   2     ,     A   1     ,   t   =     t   2         ,         TOA       A   2     ,     A   2     ,   t   =     t   2                      that pertains to the same first or second broadcast message; 
- the location server, using at least two of the calculated TDOA values          TDOA       A   1     ,     A   1     ,     A   2     ,   t   =     t   1                pertaining to the broadcast messages broadcast by a respective one of the first and second location anchor, respectively, determining first and second set of parameters that define a first and a second clock model function of time, respectively, the first clock model function describing a time dependence of the TDOA values of the broadcast messages transmitted by the first location anchor only, and the second clock model function describing a time dependence of the TDOA values of the broadcast messages transmitted by the second location anchor only; 
- the location server calculating the instantaneous phase difference            C   ^         A   1     ⁢     A   2           t            from the determined first and second clock model functions and from a time elapsed between a reference point in time and the desired point in time t.