Apparatus and method for instantaneous reacquisition in a network system

• US 6,501,808 B1
• Filed: 04/29/1999
• Issued: 12/31/2002
• Est. Priority Date: 04/29/1999
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Northrop Grumman Corporation
• Inventors: Zscheile, John Walter Jr.
• Primary Examiner(s): PHU, PHUONG M
• Application Number:
  US09/301,950
• Time in Patent Office: 1,342 Days
• Field of Search: 375/130, 375/219, 375/259, 375/354, 375/356, 375/357, 375/358, 375/362, 370/503, 370/508, 370/507, 370/519, 455/427, 455/430, 455/431, 455/13.2, 455/500, 455/502, 455/503, 342/357.12, 342/357.06
• US Class Current: 375/356
• CPC Class Codes: H04B 7/18504 Aircraft used as relay or high altitude atmospheric platform

Abstract

A data link network system comprising a central node airborne station and a plurality of ground stations each having multi-channel transmitter/receiver capable of transmitting quadrature phase spread spectrum signals and in phase spread spectrum signals both of which contain data. One of said quadrature channels is maintained as a master channel which provides a master time of day clock in the airborne platform of the network system and the other channel is employed as an adjustable time of day clock channel for resynchronizing ground stations after an outage. When an outage occurs between the airborne station and one of the ground stations the airborne station calculates the propagation time to the ground station and shifts the adjustable channel to transmit a spread spectrum data signal which will arrive in synchronization with the time of day in the ground station that had the outage. The transmitted data signal is instantaneously reacquired by the ground station and the data transmitted is employed to resynchronize the ground station receiver/transmitter with the master clock in the airborne receiver/transmitter.

Claims

1. Apparatus in a data link network system of the tying having a central node and a plurality of ground stations each having a transmitter/receiver for maintaining spread spectrum communications on the network, comprising:

a transmitter in said central node having a multi-channel transmitter for transmitting multichannel of quadrature and in phase spread spectrum data signals,

one of the said multi-channels providing a fixed master time of day clock for said data link network system,

the other of said multi-channels providing an adjustable time of day clock relative to said meter time of day clock,

control means in said central node for sensing an outage between said central node and a ground station,

said control means in said central node for calculating a propagation time T1 to said ground station,

said control means in said central node for adjusting the timing of one of said spread spectrum signals to the transmitted relative to said master clock so that the adjusted signal is synchronized with the spread spectrum receiver in said ground station, and means in said ground station receiver for instantaneously reacquiring the transmitted adjusted spread spectrum signal transmitted by said central node to said ground station.

2. Apparatus as set forth in claim 1 wherein the ground station receiver comprises means for receiving data indicative of said propagation time T1 and for calculating a ground station clock time that is resynchronized with said master clock in said central node.

3. Apparatus as set forth in claim 2 wherein the ground station transmitter comprises means for transmitting data to said central node indicative of its network status including the reacquisition is established.

4. Apparatus as set forth in claim 3 wherein said central node receiver comprises means for receiving status data from said ground station and for readjusting said adjustable channel to the same time relationship with said master clock in said central node.

5. Apparatus as set forth in claim 1 wherein said control means in said central node comprises means for determining the status of all of said ground receivers and for reestablishing acquisition of any ground station after an outage is detected.

6. Apparatus as set forth in claim 5 wherein said control means further comprises means for allocating power and data rate of the spread spectrum signals in said multi-channels when all ground stations are reacquired and no outage exists.

7. A method of reacquiring synchronization between a multi-channel central node receiver/transmitter and receiver/transmitter of a ground station after an outage, comprising the steps of:

sensing at the central node receiver/transmitter that an outage has occurred between a ground station and the central node receiver/transmitter,

sensing at the central node receiver/transmitter when the outage has been removed and an up link data signal is received,

determinating at the central node the propagation time required to spread spectrum signals to said ground station,

adjusting the relative time of the spread spectrum signals in an in phase adjustable channel of said multi-channel receiver/transmitter while maintaining a master channel with master time of day spread spectrum clock signals,

transmitting said adjusted spread spectrum signals to said ground station said adjusted spread spectrum clock signal being adjusted to arrive in synchronization with the spread spectrum clock signals in said ground station receiver,

instantaneously reacquiring said adjusted spread spectrum signals and data accompanying said adjusted spread spectrum signals, and

employing said accompanying data to reset the relative time of said spread spectrum clock signals in said ground station receiver so that subsequent spread spectrum signals from said master channel are received in synchronization with the spread spectrum receiver in said ground station.

8. The method as set forth in claim 7 which further includes the step of transmitting from said ground station to said central node a status signal that is synchronized to arrive at said central node at a predetermined time.

9. The method as set forth in claim 8 wherein said predetermined time comprises a unique time division multiple access time slot.

10. The method as set forth in claim 7 wherein said step of transmitting said adjusted spread spectrum signals to said ground station comprises transmitting said adjusted signals until an acknowledgement signal is received from said ground station.

11. The method as set forth in claim 10 which further includes ceasing transmittal of said adjusted signals to said ground station, and

returning said adjusted time of said spread spectrum signals in said adjustable channel to synchronization with the master time of day clock signals to said master channel.

12. The method as set forth in claim 11 which further includes the stop of controlling the power and data rate of channels of said multi-channel node independently of each other.