Automatic frequency control of satellite transmitted spread spectrum signals
First Claim
Patent Images
1. A radio communication system, comprising:
- a remote transmitter for transmitting a burst mode, direct sequence spread spectrum information signal having a carrier center frequency F1, a chip frequency α
, and a power versus frequency spectrum characterized by at least one intermediate null frequency at which the signal power has a minimum value, said null frequency occurring at F1 ±
Kα
, where K is an integer equal to or greater than 1;
a central station having a pilot signal transmitter for transmitter a pilot signal in the form of a continuous unmodulated carrier signal having a frequency substantially equal to said null frequency, and a receiver for receiving retransmitted information and pilot signals;
a signal relay for receiving the information signal from said remote transmitter and the pilot signal from said central station, and for retransmitting said information and pilot signals to the central station, said signal relay including a local oscillator which is susceptible to frequency drift; and
automatic frequency control means coupled to the receiver at said central station for detecting variations in the frequency of the received pilot signal and for adjusting the response of the receiver in accordance with said variations.
3 Assignments
0 Petitions
Accused Products
Abstract
Automatic frequency control is provided in a satellite-based spread spectrum radio communication system by employing a pilot signal as a frequency reference. A transmitter inserts the pilot signal at a null point in the power versus frequency spectrum of the transmitted spread spectrum signal in order to minimize bandwidth requirements and to avoid interference between the pilot signal and the transmitted data.
47 Citations
59 Claims
-
1. A radio communication system, comprising:
-
a remote transmitter for transmitting a burst mode, direct sequence spread spectrum information signal having a carrier center frequency F1, a chip frequency α
, and a power versus frequency spectrum characterized by at least one intermediate null frequency at which the signal power has a minimum value, said null frequency occurring at F1 ±
Kα
, where K is an integer equal to or greater than 1;a central station having a pilot signal transmitter for transmitter a pilot signal in the form of a continuous unmodulated carrier signal having a frequency substantially equal to said null frequency, and a receiver for receiving retransmitted information and pilot signals; a signal relay for receiving the information signal from said remote transmitter and the pilot signal from said central station, and for retransmitting said information and pilot signals to the central station, said signal relay including a local oscillator which is susceptible to frequency drift; and automatic frequency control means coupled to the receiver at said central station for detecting variations in the frequency of the received pilot signal and for adjusting the response of the receiver in accordance with said variations. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
-
-
15. A radio communication system for receiving a burst mode, direct sequence spread spectrum information signal from a remote transmitter, said information signal having a carrier center frequency F1 a chip frequency α
- , and a power versus frequency spectrum characterized by at least one intermediate null frequency at which the signal power has a minimum value, said null frequency occurring at F1 ±
Kα
, where K is an integer equal to or greater than 1, said communication system comprising;a central station having a pilot signal transmitter for transmitting a pilot signal in the form of a continuous unmodulated carrier signal having a frequency substantially equal to said null frequency, and a receiver for receiving retransmitted information and pilot signals; a signal relay for receiving the information signal from said remote transmitter and the pilot signal from said central station and for retransmitting said information and pilot signals to the central station, said signal relay including a local oscillator which is susceptible to frequency drift; and automatic frequency control means coupled to the receiver at said central station for detecting variations in the frequency of the received pilot signal and for adjusting the response of the receiver in accordance with said variations. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28)
- , and a power versus frequency spectrum characterized by at least one intermediate null frequency at which the signal power has a minimum value, said null frequency occurring at F1 ±
-
29. A radio communication system for receiving a burst mode, direct sequence spread spectrum information signal from a remote transmitter through a signal relay having a local oscillator which is susceptible to frequency drift, said information signal having a carrier center frequency F1, a chip frequency α
- , and a power versus frequency spectrum characterized by at least one intermediate null frequency at which the signal power has a minimum value, said null frequency occurring at F1 ±
Kα
, where K is an integer equal to or greater than 1, said communication system comprising;a pilot signal transmitter for transmitting to said signal relay a pilot signal in the form of a continuous unmodulated carrier signal having a frequency substantially equal to said null frequency; a receiver for receiving retransmitted information and pilot signals from said signal relay; automatic frequency control means coupled to said receiver for detecting variations in the frequency of the received pilot signal and for adjusting the response of the receiver in accordance with said variations. - View Dependent Claims (30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40)
- , and a power versus frequency spectrum characterized by at least one intermediate null frequency at which the signal power has a minimum value, said null frequency occurring at F1 ±
-
41. A method for transmitting an information signal from a transmitting station to a receiving station through a signal relay having a local oscillator which is subject to frequency drift, said method comprising the steps of:
-
transmitting a burst mode, direct sequence spread spectrum information signal from said transmitting station to said signal relay, said information signal having a carrier center frequency F1, a chip frequency α
, and a power versus frequency spectrum characterized by at least one intermediate null frequency at which the signal power has a minimum value, said null frequency occurring at F1 ±
Kα
, where K is an integer equal to or greater than 1;receiving the information signal at said signal relay and retransmitting said information signal to the receiving station; transmitting a pilot signal to the signal relay, said pilot signal comprising a continuous unmodulated carrier signal having a frequency substantially equal to the null frequency of the transmitted information signal; receiving the pilot signal at said signal relay and retransmitting said pilot signal to the receiving station; receiving the retransmitted information and pilot signals at the receiving station; detecting variations in the frequency of the pilot signal received at the receiving station; and carrying out automatic frequency control at the receiving station based on said detected variations. - View Dependent Claims (42, 43, 44, 45, 46, 47, 48, 49, 50)
-
-
51. A method for carrying out automatic frequency control of a burst mode, direct sequence spread spectrum information signal received at a receiving station from a transmitting station through a signal relay having a local oscillator which is subject to frequency drift, said information signal having a carrier center frequency F1, a chip frequency α
- , and a power versus frequency spectrum characterized by at least one intermediate null frequency at which the signal power has a minimum value, said null frequency occurring at F1 ±
Kα
, where K is an integer equal to or greater than 1, said method comprising the steps of;transmitting a pilot signal to the signal relay, said pilot signal comprising a continuous unmodulated carrier signal having a frequency substantially equal to the null frequency of the transmitted information signal; receiving the pilot signal at said signal relay and retransmitting the pilot signal to the receiving station; receiving the information signal and the retransmitting pilot signal at the receiving station; detecting variations in the frequency of the pilot signal received at the receiving station; adjusting the response of receiving equipment at the receiving station in accordance with said detected variations. - View Dependent Claims (52, 53, 54, 55, 56, 57, 58, 59)
- , and a power versus frequency spectrum characterized by at least one intermediate null frequency at which the signal power has a minimum value, said null frequency occurring at F1 ±
Specification