Initial acquisition of synchronization for a station in a TDMA satellite communication network

• US 4,346,470 A
• Filed: 03/21/1980
• Issued: 08/24/1982
• Est. Priority Date: 03/21/1980
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Shabe, John, Alvarez, Joseph A. III
• Primary Examiner(s): Britton, Howard
• Application Number:
  US06/132,708
• Time in Patent Office: 886 Days
• Field of Search: 370/104, 455/12
• US Class Current: 370/324
• CPC Class Codes: H04B 7/2126 using a reference station

Abstract

A method and apparatus are disclosed for acquiring transmit synchronization at a secondary station with the periodic frame reference bursts from a reference station in a TDMA network in an improved manner to enable the use of full power initial acquisition bursts while also reducing the bandwidth required to complete the initial acquisition operation. During the first phase, the apparatus at the secondary station bursts an initial acquisition burst during a relatively wide interval in the traffic portion of a TDMA frame and measures a propagation delay factor. The apparatus then adds the propagation delay factor to the receive frame timing synchronized with the reception of the frame reference bursts at the secondary station to obtain a more accurate adjusted transmit frame timing. The more accurate frame timing is then employed in a second phase to burst a transmit reference burst from the secondary station during a relatively narrower interval in the control portion of periodic, non-consecutive ones of the TDMA frames and the apparatus measures a propagation delay correction factor. The propagation delay correction factor is then used to adjust the phase of the transmit frame timing so as to maintain the synchronization of the secondary station with the reference station. At the end of the second phase the secondary station'"'"'s normal traffic transmission operations can take place, with the transmit reference burst being periodically transmitted in the control portion of non-consecutive TDMA frames in order to achieve a long-term maintenance of synchronization between the secondary station and the reference station. The dual use of the traffic portion assigned to the secondary station for both the coarse adjustment of the transmit clocks of the station during the first phase and the transmission of normal traffic from this or other stations during the second phase of transmit acquisition for the station enables the use of a full power initial acquisition burst, while reducing the overall bandwidth requirements for the acquisition operation by completing the function with the transmit reference burst which requires substantially less bandwidth due to its narrower assigned interval and less frequent transmission.

Claims

1. In a TDMA satellite communications network having a master station and a plurality of subsidiary earth stations, each communicating through a satellite transponder in a plurality of TDMA frames grouped in a superframe, each frame having a control portion and a traffic portion, a method for achieving acquisition of synchronization with the ongoing operation of the network, by a given station, comprising the steps of:

receiving from said master station an assigned initial acquisition time slot in said traffic portion of said TDMA frame;

transmitting consecutive initial acquisition bursts in the central portion of said assigned time slot in consecutive ones of said TDMA frames;

measuring the round trip time of said initial acquisition bursts between said given station and said satellite;

adjusting, in response to said measurements, the transmission timing at said given station for variations in said satellite'"'"'s relative distance;

receiving from said master station an assigned transmit reference burst time slot which is narrower than said initial acquisition time slot, in said control portion of one of said plurality of TDMA frames in said superframe;

terminating the transmission of said initial acquisition burst and commencing transmission of said transmit reference burst in said control portion in said one of said TDMA frames to refine the local transmit timing in said given station;

transmitting said transmit reference burst from said given station in said assigned time slot of said control field of said one of said TDMA frames on an interleaved basis with the transmission of transmit reference bursts by other earth stations in said network in said assigned time slot of said control field of other ones of said TDMA frames in said superframe;

whereby the bandwidth of said TDMA frames is conserved.

2. A method for acquiring transmit synchronization at a secondary station with the periodic frame reference bursts from a reference station in a TDMA network, comprising the steps of:

bursting an initial acquisition burst from said secondary station during a relatively wide interval in the traffic portion of a TDMA frame and measuring a propagation delay factor;

adding said propagation delay factor to the receive frame timing synchronized with the reception of said frame reference bursts at said secondary station to obtain a finely adjusted transmit frame timing;

bursting a transmit reference burst from said secondary station during a relatively narrow interval in the control portion of periodic, non-consecutive ones of said TDMA frames and measuring a propagation delay correction factor;

adjusting the phase of said transmit frame timing with said correction factor to maintain synchronization of said secondary station with said reference station.

3. In a TDMA satellite communication network having a reference station transmitting periodic frame reference bursts defining the beginning of consecutive TDMA frames, each frame having a control signal portion and a traffic portion, a plurality of said frames grouped into periodic superframes, a method for acquiring transmit acquisition of synchronization at a secondary station in the network, comprising the steps of:

synchronizing a receive clock at said secondary station by starting a receive frame when said frame reference burst is received;

adding an estimated satellite round trip propagation delay factor to the start of said receive frame during a first phase of transmit acquisition to start a transmit frame, to coarsely synchronize a transmit clock;

bursting an initial acquisition burst from said secondary station during an assigned relatively wide interval in said traffic portion of a plurality of consecutive ones of said TDMA frames;

measuring a round trip propagation delay factor for said initial acquisition bursts;

adding said round trip propagation delay factor to the start of said receive frame to start said transmit frame, to finely adjust said transmit clock;

bursting a transmit reference burst from said secondary station during an assigned relatively narrow interval in said control portion of one of said frames in said perodic superframes, during a second phase of transmit acquisition;

measuring a round trip propagation delay factor for said transmit reference bursts with said transmit clock and deriving a correction factor therefrom;

adjusting the speed of said transmit clock with said correction factor to maintain a precise synchronization of said transmit clock with the transmit clock at said reference station.

4. In a TDMA satellite communications network having a master station and a plurality of subsidiary earth stations, each communicating through a satellite transponder in a plurality of TDMA frames grouped in a superframe, each frame having a control portion and a traffic portion, an apparatus for achieving acquisition of synchronization with the ongoing operation of the network, by a secondary station, comprising:

receiving means at said secondary station, for receiving from said master station an assigned initial acquisition time slot in said traffic portion of said TDMA frame;

transmission means connected to said receiving means, for transmitting consecutive initial acquisition bursts in the central portion of said assigned time slot in consecutive ones of said TDMA frames;

delay measuring means connected to said receiving means, for measuring the round trip time of said initial acquisition bursts between said secondary station and said satellite;

timing adjustment means connected to said measuring means, for adjusting, in response to said measurements, the transmission timing at said secondary station for variations in said satellite'"'"'s relative distance;

said receiving means receiving from said master station an assigned transmit reference burst time slot which is narrower than said initial acquisition time slot, in said control portion of one of said plurality of TDMA frames in said superframe;

said transmission means terminating the transmission of said initial acquisition burst and commencing transmission of said transmit reference burst in said control portion in said one of said TDMA frames;

phase adjustment means connected to said transmission means to control transmitting said transmit reference burst from said secondary station in said assigned time slot of said control field of said one of said TDMA frames on an interleaved basis with the transmission of transmit reference bursts by other earth stations in said network in said assigned time slot of said control field of other ones of said TDMA frames in said superframe to refine the local transmit timing in said secondary station;

whereby the bandwidth of said TDMA frame is conserved.

5. An apparatus for acquiring transmit synchronization at a secondary station with the periodic frame reference bursts from a reference station in a TDMA network, comprising:

a first transmission means at said secondary station, for bursting an initial acquisition burst during a first phase from said secondary station during a relatively wide interval in the traffic portion of a TDMA frame and measuring a propagation delay factor;

a timing adjustment means connected to said first transmission means, for adding said propagation delay factor to the receive frame timing synchronized with the reception of said frme reference bursts at said secondary station to obtain a finely adjusted transmit frame timing;

a second transmission means connected to said timing adjustment means, for bursting a transmit reference burst after said first phase from said secondary station during a relatively narrow interval in the control portion of periodic, non-consecutive ones of said TDMA frames and measuring a propagation delay correction factor;

a phase adjustment means connected to said second transmission means, for adjusting the phase of said transmit frame timing with said correction factor to maintain synchronization of said secondary station with said reference station.

6. In a TDMA satellite communication network having a reference station transmitting periodic frame reference bursts defining the beginning of consecutive TDMA frames, each frame having a control signal portion and a traffic portion, a plurality of said frames grouped into periodic superframes, an apparatus for acquiring transmit acquisition of synchronization at a secondary station in the network, comprising the steps of:

a receive clock synchronizing means for synchronizing a receive clock at said secondary station by starting a receive frame when said frame reference burst is received;

a delay estimating means connected to said receive clock synchronizing means, for adding an estimated satellite round trip propagation delay factor to the start of said receive frame during a first phase of transmit acquisition to start a transmit frame, to coarsely synchronize a transmit clock;

a first transmission means connected to said delay estimating means, for bursting an initial acquisition burst from said secondary station during an assigned relatively wide interval in said traffic portion of a plurality of consecutive ones of said TDMA frames;

a delay measuring means connected to said first transmission means, for measuring a round trip propagation delay factor for said initial acquisition bursts;

a timing adjustment means connected to said delay measuring means, for adding said round trip propagation delay factor to the start of said receive frame to start said transmit frame, to finely adjust said transmit clock;

a second transmission means connected to said timing adjustment means, for bursting a transmit reference burst from said secondary station during an assigned relatively narrow interval in said control portion of one of said frames in said periodic superframes, during a second phase of transmit acquisition;

a phase measuring means connected to said second transmission means, for measuring a round trip propagation delay factor for said transmit reference bursts with said transmit clock and deriving a correction factor therefrom;

a phase adjustment means connected to said phase measuring means, for adjusting the phase of said transmit clock with said correction factor to maintain a precise synchronization of said transmit clock with the transmit clock at said reference station.