Method and apparatus for mitigating the effects of a communications channel using polarized signals

• US 6,185,408 B1
• Filed: 09/03/1997
• Issued: 02/06/2001
• Est. Priority Date: 09/03/1997
• Status: Expired due to Term

• Current Assignee: CDC Propriete Intellectuelle
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Leopold, Raymond Joseph, Ibanez-Meier, Rodrigo, Turcotte, Randy Lee
• Primary Examiner(s): Urban, Edward F.
• Assistant Examiner(s): TRAN, CONGVAN
• Application Number:
  US08/927,149
• Time in Patent Office: 1,252 Days
• Field of Search: 455/12.1, 455/427, 455/303, 455/312, 455/10, 455/295, 455/60, 455/296, 455/67.3, 455/63, 455/70, 342/361, 342/365, 342/362, 370/500, 370/491, 375/346, 375/349
• US Class Current: 455/12.1
• CPC Class Codes: H04B 7/18513 Transmission in a satellite or space-based system
• CPC Class Codes: H04B 7/195 Non-synchronous stations

Abstract

A method and apparatus for rapidly characterizing a communications channel is used to mitigate the effects of the communications channel as present in a received signal. A satellite (20) transmits a data signal (40) and a pilot signal (50). The data signal (40) and the pilot signal (50) are substantially orthogonally polarized. A user terminal (30) receives the orthogonally polarized data signal (40) and pilot signal (50). The user terminal includes a channel information recovery circuit (250) and a channel effects mitigation circuit (240). The channel information recovery circuit (250) characterizes the communications channel by analyzing the pilot signal (50), and then provides the channel information (260) to the channel effects mitigation circuit (240) which then mitigates the effects of the channel.

Claims

1. A method of dynamically reducing the effects of distortion in a communications channel between a satellite in low-Earth orbit and and a ground station wherein the satellite is moving rapidly with respect to the ground station resulting in rapid changes in said communications channel, said method comprising the steps of:

transmitting from the satellite a data signal having a first linear polarization;

transmitting from said the satellite a pilot signal having a second linear polarization orthogonal to the first polarization, said pilot signal signal having a same frequency as said data signal;

receiving at said ground station said pilot signal and said data signal through said communications channel, the pilot signal and data signal received by the ground station having channel distortion;

extracting channel distortion information from said pilot signal by comparing the received pilot signal with pilot signal information stored in the ground station; and

mitigating channel effects on said data signal using said channel distortion information.

2. The method of claim 1 further comprising the steps of:

the ground station transmitting said channel distortion information to said satellite;

the satellite applying pre-distortion to said said data signal prior to transmitting said data signal, said predistortion compensating at least in part for said channel distortion imparted on said data signal by the communications channel; and

repeating the steps of extracting and mitigating during the rapid movement of said satellite in low-earth orbit thereby dynamically compensating for distortion in the communications channel.

3. The method of claim 2 wherein said pilot signal comprises a predetermined data sequence known by said ground station.

4. The method of claim 3 wherein the receiving step comprises the step of receiving the pilot signal and the data signal with a phased-array antenna.

5. The method of claim 4 wherein said extracting step comprises the step of determining inverse channel filter coefficients.

6. The method of claim 5 wherein said mitigating step comprises the step of filtering said data signal using said inverse channel filter coefficients to reduce an amount of mean-square and peak distortion, said filtering step being performed with a transverse filter having time-delay taps.

7. A satellite communication system that dynamically reduces the effects distortion in a communications channel comprising:

a ground station; and

a transmitter located on a rapidly moving low-earth orbiting satellite linked with said sound station by the communications channel, wherein rapid changes in said communications channel are caused by the rapid movement of the satellite resulting in distortion,

wherein the ground station comprises;

a receiver for receiving a data signal having a first linear polarization and a pilot signal having a second linear polarization, said first linear polarization and said second linear polarization being substantially orthogonal, said data signal and said pilot signal being received through said communications channel from the transmitter, the data signal and the pilot signal having the same frequency;

a channel effects mitigation circuit coupled to said receiver, wherein said channel effects mitigation circuit mitigates channel effects on said data signal using channel distortion information extracted from said pilot signal;

a channel information recovery circuit coupled between said receiver and said channel effects mitigation circuit, wherein said channel information recovery circuit extracts said channel distortion information from the received pilot signal by comparing the received pilot signal with pilot signal information stored in the ground station,

whereby the channel information recovery circuit extracts said channel distortion information and the chanel effects mitigation circuit mitigates said channel effect as the satellite moves rapidly with respect to the ground station thereby dynamically compensating for distortion in the communications channel.

8. The satellite communication system of claim 7 wherein the channel distortion information comprises inverse channel filter coefficients and said channel effects mitigation circuit comprises a transverse filter having time-delay taps for reducing an amount of mean-square and peak distortion present in the received data signal.

9. The satellite communication system of claim 8 wherein the ground station further comprises a ground station transmitter for transmitting the channel distortion information to the satellite and the satellite applies pre-distortion to said said data signal prior to transmitting said data signal, said predistortion being based on the channel distortion information, whereby said predistortion compenstates in part for said channel distortion imparted on said data signal by the communications channel.

10. The satellite communication system of claim 9 wherein said said pilot signal comprises a predetermined data sequence known by the channel information recovery circuit.

11. The satellite communication system of claim 10 wherein said ground station further comprises a phased-array antenna for receiving the data signal and the pilot signal from the satellite.

12. The satellite communication system of claim 11 wherein said channel information recovery circuit comprises a digital processor.