GPS POSITIONING SYSTEM

1 . A method, comprising:

receiving identification of a global positioning system (GPS) channel by at least one terrestrial beacon, where the GPS channel is not assigned to any GPS satellite which is currently within a field of view of a reference receiver; and

transmitting signals from the at least one terrestrial beacon over the identified GPS channel.

2 . The method of claim 1 , wherein the transmitting step is performed using a format used by a specific GPS satellite which uses the identified GPS channel to broadcast its ephemeris.

3 . The method of claim 2 , wherein the signals are transmitted from the at least one terrestrial beacon using a CDMA code which is same as a CDMA code used by the specific GPS satellite.

4 . The method of claim 1 , further comprising:

using the reference receiver to search for GPS signals from one or more GPS satellites,

identifying from which GPS satellites the GPS signals are received by the reference receiver; and

determining that the specific GPS satellite is not within a field of view of the reference receiver based on whether any GPS signals are received from the specific GPS satellite.

5 . The method of claim 1 , further comprising:

determining one or more reserved GPS channels which is not currently assigned to any GPS satellite;

wherein the identified GPS channel is from among the one or more reserved GPS channels.

6 . The method of claim 1 , wherein the signals transmitted from the at least one terrestrial beacon contain ephemeris data of the at least one terrestrial beacon.

7 . The method of claim 6 , further comprising encoding the position data according to an encoding used by the specific GPS satellite.

8 . The method of claim 1 , wherein a GPS receiver uses the signals transmitted from the at least one terrestrial beacon in place of signals from at least one corresponding GPS satellite, for computing a location of the GPS receiver.

9 . A method, comprising:

identifying a global positioning system (GPS) channel which is not assigned to any GPS satellite currently within a field of view of a reference receiver;

assigning the GPS channel to a terrestrial beacon, wherein the terrestrial beacon transmits ephemeris data using a format used by a GPS satellite to broadcast its ephemeris over the same GPS channel; and

transmitting assisted GPS data to be received by a GPS receiver, the assisted GPS data including ephemeris of the terrestrial beacon.

10 . The method of claim 10 , further comprising, before the transmitting step, substituting the ephemeris of the terrestrial beacon into the assisted GPS data in place of ephemeris of a GPS satellite which is assigned to the GPS channel.

11 . The method of claim 9 , wherein the information transmitted to the terrestrial beacon includes a CDMA code used by the GPS satellite for transmitting its ephemeris over the same GPS channel.

12 . The method of claim 9 , further comprising:

using the reference receiver to search for GPS signals from one or more GPS satellites,

identifying from which GPS satellites the GPS signals are received; and

determining that a specific GPS satellite is not currently within a field of view of the reference receiver based on absence of any GPS signals received from the specific GPS satellite.

13 . The method of claim 9 , further comprising:

determining one or more reserved GPS channel which is not currently assigned to any GPS satellite, wherein the identified channel is from among the one or more reserved GPS channel.

14 . A system comprising:

a processing server programmed to determine which GPS satellites are currently within a field of view of the processing server, the processing server programmed to transmit information identifying at least one GPS satellite which is not currently within view; and

at least one terrestrial beacon configured to receive the information identifying the at least one GPS satellite, and to broadcast signals over a GPS channel that is used by the at least one GPS satellite.

15 . The system of claim 14 , wherein the processing server is programmed to

search for GPS signals from one or more GPS satellites within a field of view of the processing server, and determines which channels are available based on which satellites are within the field of view,

16 . The system of claim 14 , wherein the processing server is programmed to determine one or more reserved GPS channel which is not currently assigned to any GPS satellite, wherein the determined channel is from among the one or more reserved GPS channel.

17 . The system of claim 14 , wherein the processing server transmits a CDMA code of a specific GPS satellite to the terrestrial beacon, and the terrestrial beacon is configured to transmit signals containing ephemeris data over the at least one available GPS channel using the CDMA code.

18 . The system of claim 17 , wherein the terrestrial beacon is programmed to transmit the signals using a same format used by the specific GPS satellite for broadcasting ephemeris data.

19 . The system of claim 18 , wherein the terrestrial beacon is programmed to transmit a message containing an almanac in which GPS data from at least one out-of-view satellite is replaced with data identifying the ephemeris of the terrestrial beacon.

20 . The system of claim 14 , wherein the system includes a plurality of terrestrial beacons at a plurality of locations and/or altitudes.

21 . The system of claim 20 , wherein two or more of the plurality of terrestrial beacons are included inside a building.