초록 ▼

A spread spectrum position location communication system determines the position of a mobile master radio using a round-trip messaging scheme in which the time of arrive (TOA) of ranging messages is accurately determined to yield the range estimates required to calculate the position of the mobile r

A spread spectrum position location communication system determines the position of a mobile master radio using a round-trip messaging scheme in which the time of arrive (TOA) of ranging messages is accurately determined to yield the range estimates required to calculate the position of the mobile radio via trilateration. The master radio transmits outbound ranging messages to plural reference radios which respond by transmitting reply ranging messages. Upon reception of the reply ranging message, the master radio determines the range to the reference radio from the signal propagation time calculated by subtracting the far-end turn around time from the round-trip elapsed time. Any combination of fixed or mobile radios of known positions can be used as the reference radios for another mobile radio in the system, thereby providing adaptability under varying transmission conditions. The individual radios do not need to be synchronized to a common time reference, thereby eliminating the need for highly accurate system clocks. By performing internal delay calibration, errors caused by difficult-to-predict internal transmitter and receiver delay variations can be minimized. Leading-edge-of-the-signal curve fitting and frequency diversity techniques minimize the effects of multipath interference on TOA estimates.

대표청구항 ▼

A spread spectrum position location communication system determines the position of a mobile master radio using a round-trip messaging scheme in which the time of arrive (TOA) of ranging messages is accurately determined to yield the range estimates required to calculate the position of the mobile r

A spread spectrum position location communication system determines the position of a mobile master radio using a round-trip messaging scheme in which the time of arrive (TOA) of ranging messages is accurately determined to yield the range estimates required to calculate the position of the mobile radio via trilateration. The master radio transmits outbound ranging messages to plural reference radios which respond by transmitting reply ranging messages. Upon reception of the reply ranging message, the master radio determines the range to the reference radio from the signal propagation time calculated by subtracting the far-end turn around time from the round-trip elapsed time. Any combination of fixed or mobile radios of known positions can be used as the reference radios for another mobile radio in the system, thereby providing adaptability under varying transmission conditions. The individual radios do not need to be synchronized to a common time reference, thereby eliminating the need for highly accurate system clocks. By performing internal delay calibration, errors caused by difficult-to-predict internal transmitter and receiver delay variations can be minimized. Leading-edge-of-the-signal curve fitting and frequency diversity techniques minimize the effects of multipath interference on TOA estimates. dress of a corresponding subscriber and one of the plurality of virtual circuits; a processor coupled to the memory; and a second network interface coupled to the processor; wherein the first network interface is operable to receive a communication from a source subscriber, the communication identifying a destination, and the second network interface is operable to forward the communication toward the destination if the processor determines that a particular subscriber association stored in the memory specifies the physical address of the source subscriber and the virtual circuit used to receive the communication. 2. The network device of claim 1, wherein the processor is operable to generate for storage in the memory a subscriber association specifying the physical address of the source subscriber and the virtual circuit used to receive the communication if the processor determines that the physical address of the source subscriber is not specified by any of the subscriber associations already stored in the memory. 3. The network device of claim 1, wherein the second network interface is further operable to forward the communication toward the destination if the physical address of the source subscriber is not specified by any of the subscriber associations stored in the memory. 4. The network device of claim 1, wherein the second network interface is further operable to forward the communication toward the destination if a particular subscriber association specifies the physical address of the source subscriber and does not specify any of the plurality of virtual circuits. 5. The network device of claim 1, wherein the second network interface does not forward the communication toward the destination if the physical address of the source subscriber is specified by a particular subscriber association stored in the memory and the virtual circuit used to receive the communication does not correspond to the virtual circuit specified by the particular subscriber association. 6. The network device of claim 1, wherein the communication network comprises a first communication network and the destination is associated with a second communication network. 7. The network device of claim 1, wherein the source subscriber comprises a first subscriber and the destination is associated with a second subscriber. 8. The network device of claim 1, wherein the communication indicates the physical address of the source subscriber and the virtual circuit used to receive the communication. 9. The network device of claim 1, wherein the communication network comprises an Asynchronous Transfer Mode network and each virtual circuit is identified using a virtual path identifier and a virtual channel identifier. 10. The network device of claim 1, wherein the physical address for each subscriber comprises a MAC address. 11. A method for controlling subscriber loops, comprising: receiving a communication from a source subscriber using a particular one of a plurality of virtual circuits associated with a communication network, the communication identifying a destination; storing in a memory a plurality of subscriber associations, each subscriber association specifying a physical address associated with a corresponding subscriber and one of the plurality of virtual circuits; and forwarding the communication toward the destination if a particular subscriber association specifies the physical address of the source subscriber and the virtual circuit used to receive the communication. 12. The method of claim 11, further comprising generating for storage in the memory a subscriber association specifying the physical address of the source subscriber and the virtual circuit used to receive the communication if the physical address of the source subscriber is not specified by any of the subscriber associations already stored in the memory. 13. The method of claim 11, further comprising forwarding the communication toward the destination if the physical a