Synchronization method and apparatus for multi-platform communication system

• US 6,757,546 B1
• Filed: 08/21/2000
• Issued: 06/29/2004
• Est. Priority Date: 03/18/1999
• Status: Expired due to Term

• Current Assignee: DIRECTV, LLC (AT&T, Inc.)
• Original Assignee: The DIRECTV Group, Inc. (AT&T, Inc.)
• Inventors: Chang, Donald C. D., Feria, Ying, Yung, Kar W., Hagen, Frank A.
• Primary Examiner(s): Trost, William
• Assistant Examiner(s): Le, Danh C
• Application Number:
  US09/644,225
• Time in Patent Office: 1,408 Days
• Field of Search: 455/502, 455/13.2, 455/12.1, 455/11.1, 455/3.01, 370/315, 370/316, 370/324, 370/320, 370/321, 370/319, 375/145, 375/140
• US Class Current: 455/502
• CPC Class Codes: H04B 7/18504 Aircraft used as relay or high altitude atmospheric platform
• CPC Class Codes: H04B 7/18506 Communications with or from aircraft, i.e. aeronautical mobile service
• CPC Class Codes: H04B 7/18532 Arrangements for managing transmission, i.e. for transporting data or a signalling message
• CPC Class Codes: H04B 7/18534 for enhancing link reliablility, e.g. satellites diversity
• CPC Class Codes: H04B 7/212 Time-division multiple access [TDMA]

Abstract

A mobile wireless communications system including a plurality of individual transponding nodes of various types, all in communication with a central processing hub. A local user signal is processed by the central processing hub and radiated through multiple paths to a plurality of the plurality of individual transponding platforms simultaneously. The signal is then re-radiated by each of the plurality of the plurality of individual transponding platforms to a mobile terminal that receives the re-radiated signal from the plurality of the plurality of individual transponding platforms coherently and in phase. The central hub synchronizes both the signals received and transmitted from each user through one or more of the transponding nodes. This synchronization is such that the relative arrival time of the PN encoded data in the user signals is synchronized to within a fraction of a chip in both the forward and return links. The central hub also synchronizes the carrier phase of the user signals to within a fraction of a wavelength in both the forward and return links.

Claims

1. A method for synchronizing a plurality of user signals such that each of the plurality of user signals arrives in-phase at the location of an intended recipient, comprising:

providing a plurality of individual transponding nodes;

providing a plurality of mobile users each having a respective mobile terminal;

establishing a link between at least one of said plurality of mobile terminals and a ground hub through one or more of said plurality of transponding nodes;

transmitting one or more of said plurality of user signals to and from said central hub;

synchronizing a relative arrival time of PN encoded data contained in said one or more of said plurality of user signals to within a fraction of a chip in both a forward link and a return link; and

synchronizing a carrier phase of said one or more of said plurality of user signals to within a fraction of a wavelength in both said forward and return links.

2. The method of claim 1, wherein said relative arrival time of said user signals are related according to the following equation:

$t_{\mathrm{kn}\pm <br><br>}^{\mathrm{hub}}=t_{k\pm <br><br>}^{\mathrm{usr}}\pm <br><br>\left({\mathrm{\tau <br><br>}}_{k\pm <br><br>}^{\mathrm{hnd}}+{\mathrm{\tau <br><br>}}_{\mathrm{kn}\pm <br><br>}^{\mathrm{usr}}+{\mathrm{\tau <br><br>}}_{n\pm <br><br>}^{\mathrm{plt}}+{\mathrm{\tau <br><br>}}_{n\pm <br><br>}^{\mathrm{fdr}}+{\mathrm{\tau <br><br>}}_{n\pm <br><br>}^{\mathrm{hub}}\right).$

3. The method of claim 2, further comprising:

measuring said arrival times of the same data frame as transmitted by one of said plurality of mobile users via one or more of said plurality of transponding nodes.

4. The method of claim 3, wherein said measured arrival times are related to the time at which said data frame was sent by said user mobile terminal as follows:

${\tilde{t}}_{\mathrm{kn}-}^{\mathrm{hub}}=t_k^{\mathrm{usr}}+{\mathrm{\tau <br><br>}}_{k-}^{\mathrm{hnd}}+{\mathrm{\tau <br><br>}}_{\mathrm{kn}}^{\mathrm{usr}}+{\mathrm{\tau <br><br>}}_{n-}^{\mathrm{plt}}+{\mathrm{\tau <br><br>}}_n^{\mathrm{fdr}}+{\mathrm{\tau <br><br>}}_{n-}^{\mathrm{hub}}.$

5. The method of claim 4, further comprising:

inserting a variable delay into said return link signals by said ground hub.

6. The method of claim 5, further comprising:

determining the magnitude of said return link signal variable delay according to the following;

$\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\tau <br><br>}}_{\mathrm{kn}-}^{\mathrm{hub}}=\left({\mathrm{Max}}_n<br><br>{\tilde{t}}_{\mathrm{kn}-}^{\mathrm{hub}}\right)-{\tilde{t}}_{\mathrm{kn}-}^{\mathrm{hub}}$${\hat{t}}_{k-}^{\mathrm{hub}}=t_{\mathrm{kn}-}^{\mathrm{hub}}+\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\tau <br><br>}}_{\mathrm{kn}-}^{\mathrm{hub}}={\mathrm{Max}}_n<br><br>{\tilde{t}}_{\mathrm{kn}-}^{\mathrm{hub}}.$

7. The method of claim 2, further comprising:

determining any processing delay between said forward link signals and said return link signals.

8. The method of claim 1, wherein said synchronizing said carrier phase in said return link further comprises adding a phase estimation and removal function to the processing of said one or more of said plurality of user signals.

9. The method of claim 1, wherein said synchronizing said carrier phase in said forward link includes transmitting a calibration signal to one or more of said plurality of mobile users, measuring its phase, and returning the measured results to said ground hub.

10. The method of claim 1, wherein each of said plurality of individual transponding nodes is independently selected from one of the following system types:

a space-based system, a high altitude platform system, or a tower based cellular network.

11. A multi-platform mobile wireless communication system, comprising:

a plurality of individual transponding nodes each having a platform processor;

a plurality of mobile terminals each having a handset processor;

a central hub for establishing links with one or more of said plurality of mobile terminals and for synchronizing one or more associated user signals in both forward links and return links through one or more of said plurality of transponding platforms;

a central hub processor associated with said central hub for synchronizing the timing of PN encoded waveforms and the associated carrier phases of a user signal received or transmitted through one or more transponding platforms.

12. The system of claim 11, wherein the timing of said PN encoded waveform is synchronized to within a fraction of a chip.

13. The system of claim 12, wherein said carrier phase is synchronized to within a fraction of a wavelength.

14. The system of claim 13, wherein the timing of said PN encoded waveforms is synchronized in accordance with the following:

$t_{\mathrm{kn}\pm <br><br>}^{\mathrm{hub}}=t_{k\pm <br><br>}^{\mathrm{usr}}\pm <br><br>\left({\mathrm{\tau <br><br>}}_{k\pm <br><br>}^{\mathrm{hnd}}+{\mathrm{\tau <br><br>}}_{\mathrm{kn}\pm <br><br>}^{\mathrm{usr}}+{\mathrm{\tau <br><br>}}_{n\pm <br><br>}^{\mathrm{plt}}+{\mathrm{\tau <br><br>}}_{n\pm <br><br>}^{\mathrm{fdr}}+{\mathrm{\tau <br><br>}}_{n\pm <br><br>}^{\mathrm{hub}}\right).$

15. The system of claim 14, wherein said central hub processor incorporates a variable delay into said return link signals for synchronization, the magnitude of which is determined in accordance with the following:

$\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\tau <br><br>}}_{\mathrm{kn}-}^{\mathrm{hub}}=\left({\mathrm{Max}}_n<br><br>{\tilde{t}}_{\mathrm{kn}-}^{\mathrm{hub}}\right)-{\tilde{t}}_{\mathrm{kn}-}^{\mathrm{hub}}$${\hat{t}}_{k-}^{\mathrm{hub}}=t_{\mathrm{kn}-}^{\mathrm{hub}}+\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\tau <br><br>}}_{\mathrm{kn}-}^{\mathrm{hub}}={\mathrm{Max}}_n<br><br>{\tilde{t}}_{\mathrm{kn}-}^{\mathrm{hub}}.$

16. The system of claim 14, wherein for transmission of said forward link signals, said central hub processor determines a difference between the original time of said forward link signal and the reception time of said return link signal in accordance with the following:

${\stackrel{\_}{t}}_{k_0<br><br>n}^{\mathrm{proc}}=t_{k_0}^{\mathrm{usr}}+\frac{1}{2}<br><br>\left({\mathrm{\tau <br><br>}}_{k_0-}^{\mathrm{hnd}}-{\mathrm{\tau <br><br>}}_{k_0+}^{\mathrm{hnd}}\right)+\frac{1}{2}<br><br>\left({\mathrm{\tau <br><br>}}_{n-}^{\mathrm{plt}}-{\mathrm{\tau <br><br>}}_{n+}^{\mathrm{plt}}\right)+\frac{1}{2}<br><br>\left({\mathrm{\tau <br><br>}}_{n-}^{\mathrm{hub}}-{\mathrm{\tau <br><br>}}_{n+}^{\mathrm{hub}}\right).$

17. The system of claim 16, wherein said forward link signals are synchronized by said central hub processor in accordance with the following:

$\begin{array}{c}{\hat{t}}_{\mathrm{kn}}^{\mathrm{hub}}=\text{\hspace{1em}<br><br>}<br><br>2<br><br>{\stackrel{\_}{t}}_{k_0<br><br>n}^{\mathrm{proc}}-{\hat{t}}_{\mathrm{kn}-}^{\mathrm{hub}}\\ =\text{\hspace{1em}<br><br>}<br><br>2<br><br>{\stackrel{\_}{t}}_{k_0<br><br>n}^{\mathrm{proc}}+\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\tau <br><br>}}_{\mathrm{kn}-}^{\mathrm{hub}}-{\hat{t}}_{k-}^{\mathrm{hub}}.\end{array}$

18. The system of claim 13, wherein during the synchronization of the carrier phase in said forward link, said central hub processor probes the phase of said user signals and distinguishes the phases of said signals arriving at the user terminal via each of said plurality of transponder nodes.

19. The system of claim 18, wherein said central hub processor probes the phase of said signal arriving at a given mobile terminal in accordance with one of the following methods:

global, multi-channel, multi-cell, multi-color, or scanning.

20. A method for receiving and transmitting user signals in both a forward link and a return link in a mobile wireless communication system, comprising:

providing a plurality of individual transponding nodes each having a platform processor;

providing a plurality of mobile terminals each having a handset processor;

establishing links between a central hub and one or more of said plurality of mobile terminals through one or more of said plurality of transponding nodes;

processing a plurality of signals at said central hub for both said forward link and said return link;

processing said forward link signals such that the timing of a PN encoded waveform is synchronized and such that a phase of one or more of a plurality of user signals is probed; and

processing said return link signals such that the carrier phase is synchronized.