Method of synchronizing satellite switched CDMA communication system

• US 5,838,669 A
• Filed: 08/28/1996
• Issued: 11/17/1998
• Est. Priority Date: 08/28/1996
• Status: Expired due to Term

• Current Assignee: AT&T Corporation (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Gerakoulis, Diakoumis Parissis
• Primary Examiner(s): Patel, Ajit
• Application Number:
  US08/704,041
• Time in Patent Office: 811 Days
• Field of Search: 370/342, 370/350, 370/320, 370/335, 370/316, 370/514, 370/515, 370/519, 375/206, 375/207, 375/208, 375/209, 375/205, 375/210, 375/362, 375/364, 375/367, 375/371, 375/373, 375/374, 375/375, 375/376, 375/359
• US Class Current: 370/320
• CPC Class Codes: H04B 7/216 Code division or spread-spectrum multiple access [CDMA, SSMA]

Abstract

Synchronization of a terrestrial transmitted CDMA signal with despreading and respreading in a remote satellite, for transmission to a second terrestrial site, is achieved in accord with the processes recited in the appended claims. Uplink access and synchronization signals are acquired at a satellite switch and a reference propagation delay time is established in terms of quantified timing marks with intervals within a size range of chip intervals used in the CDMA spreading codes of the system. The propagation delay is defined in terms of one of the quantified timing marks defining when a first signal from a terrestrial subscriber unit is received. This propagation delay is transmitted to a terrestrial subscriber unit and utilized to adjust the timing of uplink CDMA code chips.

Claims

1. A method of synchronizing CDMA processing in a satellite communication system connecting multi-point ground stations, comprising the steps of:

acquiring access and Synchronization signals transmitted by a satellite at a terrestrial subscriber unit;

setting a reference propagation delay time;

establishing a propagation delay in terms of arrival of a message in relation to one of a plurality of quantified timing marks subsequent to the reference propagation delay time, when the satellite receives a first signal from the terrestrial subscriber unit on an access channel;

conveying the established quantified propagation delay to the terrestrial subscriber unit;

adjusting timing of uplink CDMA code chips at the terrestrial subscriber unit from the original reference propagation delay derived from the access channel;

tracking synchronizing by adjusting code delay of the uplink arrival time of a reference code; and

retaining synchronization by downlink code delay transmission.

2. A method of synchronizing CDMA processing in a satellite communication system connecting multi-point ground stations, as claimed in claim 1, wherein:

the step of;

establishing a propagation delay includes the steps of;

generating a sequence of quantified delays; and

locating in time an arrival of an access message between a pair of adjacent ones of the sequence of quantified delays.

3. A method of synchronizing CDMA processing in a satellite communication system connecting multi-point ground stations, as claimed in claim 1, wherein:

the step of adjusting timing includes the steps of;

determining the propagation delay difference; and

advancing the code chips by the number of chip intervals in the propagation delay difference.

4. A method of synchronizing CDMA processing in a satellite communication system connecting multi-point ground stations, as claimed in claim 1, wherein:

the step of tracking synchronization includes the steps of;

premature despreading of the uplink signal;

delayed spreading of the uplink signal; and

combining the premature and delayed spreading results.

5. A method of synchronizing CDMA processing in a satellite communication system connecting multi-point ground stations, as claimed in claim 4, wherein:

the step of tracking synchronization includes the step of;

clocking the spreading of downlink signals in response to the combined premature and delayed spreading results.

6. A method of providing synchronization of code sequences between a satellite and a ground station, comprising the steps of:

acquiring at the ground station synchronization with a pilot PN code sequence transmitted by the satellite;

acquiring at the ground station a synchronization channel providing a pilot phase offset for a specified beam, for orthogonal codes of a paging channel and for PN code sequences of a related access channel;

responding to a message arrival at the satellite to establish a propagation delay difference from a reference arrival time and sending the delay difference to the ground station;

using the delay difference at the ground station to establish a first coarse synchronization with the reference arrival time; and

inaugurating a tracking procedure at the satellite in response to a signal from the ground station to provide fine alignment of code with the reference arrival time at the despreaders within the satellite.

7. In a communication system in which a ground station transmits a CDMA beam to a satellite receiver which code switches the beam for re-transmission to a receiving ground station, a method of synchronizing the system by controlling timing of all beam PN spreading codes to have a common starting time, including the steps of:

synchronizing a ground station to a pilot PN sequence transmitted by the satellite upon a turn-on of the ground station;

acquiring at the ground station a sync channel from the satellite which provides a pilots phase offset;

transmitting an uplink signal from the ground station to the satellite to acquire a propagation delay difference derived from a satellite reference arrival time and transmitting the propagation delay difference from the satellite to the ground station;

establishing a coarse synchronization at the ground station to the satellite reference arrival time by using the propagation delay difference to advance or delay by a number of chips the starting point of an uplink beam code transmitted from the ground station to the satellite;

adding timing jitter to downlink signals from the satellite to the ground station;

tracking downlink signal transmissions which include the controlled timing jitter to make a timing adjustment to uplink transmissions from the ground station to the satellite.

8. A method of globally synchronizing CDMA signaling between at least one of a plurality of fixed location ground radio stations and a geostationary satellite radio station, comprising the steps of:

transmitting from the satellite station to the ground radio station acquisition signals to establish radio contact;

initiating a call from the ground radio station to the satellite radio station with an access channel signal to establish a propagation delay time;

transmitting the propagation delay time to the ground radio station;

over a paging channel

initiating a traffic channel connection between the ground radio station and the satellite radio station; and

transmitting propagation delay variations exhibited on a downlink traffic channel and adjusting uplink traffic channel transmissions to compensate for the variations;

whereby all of the plurality of ground stations actively transmitting, transmit substantially in synchronization with one another.

9. A method of globally synchronizing CDMA signaling between at least one of a plurality of fixed location ground radio stations and a geostationary satellite radio station, as claimed in claim 8;

where in the step of

transmitting the propagation delay time include a step of determining a delay in terms of chips of a spreading code used for CDMA encoding.

10. A method of globally synchronizing CDMA signaling between at least one of a plurality of fixed location ground radio stations and a geostationary satellite radio station, as claimed in claim 8;

where in the step of

transmitting acquisition signals includes a step of transmitting a continuous asynchronous pilot channel and a continuous asynchronous paging channel.

11. A method of globally synchronizing CDMA signaling between at least one of a plurality of fixed location ground radio stations and a geostationary satellite radio station, as claimed in claim 8;

where in the step of

adjusting uplink traffic channel transmissions includes a step of adjusting a time alignment of CDMA spreading codes.

12. A method of globally synchronizing CDMA signaling between at least one of a plurality of fixed location ground radio stations and a geostationary satellite radio station, comprising the steps of:

firstly determining and utilizing a reference propagation delay time between a ground radio station and the satellite for achieving a coarse synchronization;

secondly aligning code chips of the CDMA signaling to achieve a fine synchronization of arrival times including the reference propagation delay time of uplink signals to the satellite.

13. The method of claim 12, comprising the further steps of:

transmitting propagation delay variations exhibited on a downlink traffic channel and adjusting uplink traffic channel transmissions to compensate for the variations.

14. The method of claim 12, comprising the further steps of:

initiating a call from the ground radio station to the satellite radio station with an access channel signal to establish a propagation delay time.

15. The method of claim 12, comprising the further steps of:

maintaining a tracking procedure between satellite and ground station to maintain synchronization.

16. A method of globally synchronizing CDMA signaling between at least one of a plurality of fixed location ground radio stations and a geostationary satellite radio sation, comprising the steps of:

determining a propagation delay between a ground radio station and the satellite for achieving a coarse synchronization using access channel signals;

transmitting propagation delay variations exhibited on a downlink traffic channel and adjusting uplink traffic channel transmission using voice and data transmission to compensate for the variations; and

adjusting the timing of code chips of the CDMA signal to adjust and compensate for the variations, and achieve a fine synchronization of arrival times of uplink signals to the satellite.