Location system and method with acquisition of accurate location parameters

A method of operating a locatable unit in connection with a locator unit which moves relative to said locatable unit, said method comprising the steps of:

• receiving a first signal at said locatable unit;
• estimating a Doppler component of said first signal, said step using a preset frequency from a preset estimate table as adjusted by subsequent signals from said first one of said locator and locatable units to said second one of said locator and locatable units, said preset frequency being an approximation of propagation characteristics of said first signal;
• determining a frequency at which a second signal may be transmitted from said locatable unit so that said second signal will exhibit a predetermined frequency when received at said locator unit, said predetermined frequency being reserved for transmission of said second signal;
• and
• transmitting said second signal from said locatable unit, said second signal being modulated to convey data which describe said estimated Doppler component of said first signal.

A method of locating a locatable unit using a locator unit which resides a distance away from said locatable unit, said method comprising the steps of:

• transmitting a first signal from a first one of said locator and locatable units;
• receiving said first signal at a second one of said locator and locatable units;
• estimating, at said second unit, a propagation duration using a preset duration from said preset estimate table as adjusted by subsequent signals from said first one of said locator and locatable units to said second one of said locator and locatable units, said preset duration being an approximation of propagation characteristics required for said first signal to propagate between said first and second units;
• transmitting a second signal from said second unit, said second signal being modulated to convey data which describe said estimated propagation duration of said first signal;
• receiving said second signal at said first unit;
• measuring, at said first unit, a timing offset between a point in time at which said second signal is received at said first unit and a predetermined point in time;
• and
• determining a position for said locatable unit in response to said estimated propagation duration, received at said first unit as transmitted in said second signal and said timing offset as measured in said measuring step, said estimated propagation duration and said timing offset defining a propagation delay curve whereon said position is located.

A method of operating a locatable unit in connection with a locator unit which moves relative to said locatable unit, said method comprising the steps of:

• receiving a first signal at said locatable unit;
• estimating a propagation duration using a preset duration from a preset estimate table as adjusted by subsequent signals from said first one of said locator and locatable units to said second one of said locator and locatable units, said preset duration being an approximation of propagation characteristics required for said first signal to propagate between said locator and locatable units;
• determining a point in time at which a second signal may be transmitted from said locatable unit so that said second signal should arrive at said locator unit at a predetermined point in time;
• and
• transmitting said second signal from said locatable unit, said second signal being modulated to convey data which describe said estimated propagation duration of said first signal.

A method of operating a radio telecommunications system having at least one satellite moving in an orbit around the earth and having at least one subscriber unit located proximate the earth's surface, said method comprising the steps of:

• transmitting a first signal from said satellite;
• receiving said first signal at said subscriber unit;
• estimating, at said subscriber unit, a Doppler component of said received first signal and a propagation duration required for said first signal to propagate between said satellite and said subscriber unit;
• transmitting a second signal from said subscriber unit, said second signal being modulated to convey data which describe said estimated Doppler component of said first signal and to convey data which describe said propagation duration;
• receiving said second signal at said satellite;
• measuring, at said satellite, a frequency offset between a frequency at which said second signal is received at said satellite and a predetermined frequency, and a timing offset between a point in time at which said second signal is received at said satellite and a predetermined point in time;
• and
• determining a location of said subscriber unit relative to the earth in response to said estimated Doppler component, said estimated propagation duration, said frequency offset, and said timing offset, said estimated Doppler component and said frequency offset defining a curve whereon said location is located and said estimated propagation duration and said timing offset defining a propagation delay curve whereon said location is located.