POSITION AIDED SUBSCRIBER UNIT FOR A
SATELLITE CELLULAR SYSTEM
CROSS-REFERENCE TO RELATED 5
The present case is related to co-pending U.S. applications Ser. No. 263,849 abandoned; Ser. No. 402,743 abandoned which has the same inventive entity as the present application; Ser. No. 415.814 abandoned; Ser. No. 415,842 pending; Ser. No. 415,815 pending; and Ser. No. 414,494 pending all being assigned to the same assignee as the present invention.
BACKGROUND OF THE INVENTION 15
The present invention pertains to portable communication devices and more particularly to a position aided, portable communication device for use with a satellite communication system. 2Q
When achieving communication between satellites and users of a satellite communication system around the world, knowledge of the location of each user is important to establishing and maintaining the communication link. Knowledge of the location of a particular 25 user is also important because that location information may be reported through the satellite link which serves the user to any other user worldwide. A single unit which combines voice/data communication and precise location determination has several advantages over the 30 present day communication system devices. Applications of such a system include asset management as well as coordination of activities of search and rescue and various military operations.
Since communications of the user unit to satellites 35 involve frequent hand-offs between cells created by individual satellites and between adjacent satellites, the knowledge of precise location of both the user unit and of the satellites can be used to efficiently determine an appropriate hand-off strategy. 40
Further, precise knowledge of the location of a user unit also aids in the acquisition process by permitting precise correction for Doppler and reference frequency induced errors. The satellites of a low-earth orbit satellite communication system such as Iridium move very 45 rapidly compared with the location of a user on earth. During communications, the system must provide Doppler compensation to the signals to compensate for the rapidly changing propagation delay in the link. During acquisition of the signals, if the user unit cannot inde- 50 pendently determine the Doppler frequency, an exhaustive frequency search of the Doppler range must be performed. This length of time for an exhaustive search would delay the recognition of the user by the system. Therefore, in the case of telecommunication, the user 55 would experience a delay in being able to establish communications.
However, the communication satellite ephemerides can be stored in the user unit and will remain valid for several days. Within knowledge of the precise location 60 of the user unit, the Doppler adjustment as well as the correction to the reference oscillator can be explicitly computed. This would permit more rapid acquisition and tracking of the satellite pilot channel.
Accordingly, it is an object of the present invention 65 to provide a combined position aided voice/data communicator device for use with a satellite communication system.
SUMMARY OF THE INVENTION
In accomplishing the object of the present invention, a novel position aided voice/data subscriber unit for a satellite cellular system will be shown.
A satellite communication system includes a number of subscriber units, each subscriber unit for receiving and transmitting digital data. In addition, each subscriber unit self-determines its position.
The subscriber unit includes a receiver/transmitter for receiving from and transmitting to a satellite of the satellite communication system digital user data. In addition, the subscriber unit includes a receiver for self-determining the position of the subscriber unit and transmitting that position to the satellite of the satellite communication system.
The above and other objects, features, and advantages of the present invention will be better understood from the following detailed description taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The single sheet of drawings included herewith is a block diagram of a combined position aided subscriber unit for a satellite cellular system.
DESCRIPTION OF THE PREFERRED
The disclosure of co-pending U.S. patent applications Ser. Nos. 263,849; 402,743; 415,814; 415,842; 415,815; and 414,494 are hereby incorporated by reference.
Referring to the single sheet of drawings included herewith, antenna 1 is shown. Antenna 1 receives information from a global positioning system (GPS), not shown, as well as information transmitted from the satellites of a satellite communication system (not shown). In addition, antenna 1 operates to transmit voice and data information from the subscriber to the satellite communication system.
Antenna 1 is connected to circulator 2 which provides isolation between the transmitted and the received signals. Circulator 2 operates such that the incoming signals received from antenna 1 are transmitted to diplexer filter 3 and outgoing signal from transmittef/modulator 12 is transmitted from transmitter/modulator 12 to antenna 1 for outgoing transmission.
Diplexer filter 3 is connected to circulator 2. Diplexer filter 3 includes amplification and operates to pass both the GPS signals and satellite transmitted signals for subsequent processing. Diplexer 3 is further connected to mixer 4 and to GPS receiver 9 via path 10.
Since the GPS information as well as the transmissions from the satellite are in the same frequency band, they must be separated for processing by the communication system.
The output of mixer 4 is connected to signal discriminator 5. Signal discriminator 5 separates the satellite communication signals from all other signals received by the system. The satellite communication signals are in the L-band. which is approximately 1.5 to 1.6 GHz. Signal discriminator 5 strips, data from the carrier after determining the appropriate tracking code.
Local oscillator 6 is connected to signal discriminator 5, to digital synthesizer 8 and to GPS receiver 9. Local oscillator 6 is a reference frequency source. Signal discriminator 5 detects a reference clock error and is connected to processor 7 analogous to a phase lock loop. Such error is interpreted by the processor to adjust the