Adaptive predistortion using over-the-hop feedback

• US 5,910,965 A
• Filed: 06/30/1995
• Issued: 06/08/1999
• Est. Priority Date: 06/30/1995
• Status: Expired due to Term

• Current Assignee: BWA Technology Incorporated
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: Zakaib, Larry, Ierfino, Nick
• Primary Examiner(s): VO, DON NGUYEN
• Application Number:
  US08/496,966
• Time in Patent Office: 1,439 Days
• Field of Search: 375/296, 375/285, 375/358, 375/221, 375/222, 375/226, 375/227, 375/220, 330/149, 455/63, 455/69, 455/114, 455/115, 455/116, 455/126, 455/70, 455/71, 455/68
• US Class Current: 375/220
• CPC Class Codes: H04B 1/62 for providing a predistortion of the signal in the transmitter and corresponding correction in the receiver, e.g. for improving the signal/noise ratio

Abstract

A method and system for predistorting a signal before transmission of the signal to compensate for nonlinearities introduced when the signal is transmitted to a receiver. A signal received on a first frequency is evaluated at a receiver to determine whether the received signal includes nonlinearities without comparing the received signal to the original signal or a pilot tone. The nonlinearity data that result from the evaluation are transmitted back to the originator of the signal on a second frequency where the nonlinearity data are used to predistort signals before transmission therefrom. Communication of the nonlinearity data between transmitter and receiver at each site is through a reverse channel which is further controlled by a serial line.

Claims

1. An improved method of predistorting a signal before transmission of the signal to compensate for nonlinearities introduced when the signal is transmitted to a receiver, the improvement comprising the steps of:

(a) evaluating a received signal at a receiver to determine whether the received signal includes nonlinearities, said evaluation including the step of identifying a nonrandom distribution of data in the received signal, the nonrandom distribution being indicative of a nonlinearity; and

(b) providing a result of the evaluation back to a transmitter that sent the received signal, the result being used at the transmitter to predistort signals before transmission therefrom.

2. The method of claim 1 wherein the received signal comprises data bits and selected ones of the data bits define a constellation point, and further comprising the step of determining whether a constellation point is in an area associated with random distribution of constellation points.

3. A method of predistorting an RF signal to compensate for nonlinearities introduced when the RF signal is communicated, the method comprising the steps of:

(a) transmitting an RF signal from a first transmitter/receiver to a second transmitter/receiver on a first frequency;

(b) extracting nonlinearity data from the RF signal received at the second transmitter/receiver by

defining the nonlinearity data as constellation points related to data bits in the received RF signal;

defining an area for the constellation points that indicates when a nonlinearity has occurred; and

detecting when the constellation points fall into the defined area;

(c) transmitting a further RF signal containing the nonlinearity data from the second transmitter/receiver to the first transmitter/receiver on a second frequency; and

(d) redistorting RF signals to be transmitted from the first transmitter/receiver on the first frequency by using the received nonlinearity data.

4. The method of claim 3 wherein the step of predistorting RF signals comprises the step of:

applying predistortion corrections to RF signals to be transmitted after a predetermined number of the detections.

5. The method of claim 4 wherein the step of predistorting RF signals further comprises the steps of:

storing plural of the predistortion corrections that have been applied to RF signals and a corresponding number of the detections resulting therefrom; and

applying to RF signals to be transmitted a one of the plural predistortion corrections that provides an acceptable number of the detections.

6. The method of claim 5 wherein the steps of claim 4 are repeated in order to identify a one of the predistortion corrections that provides the least number of the detections.

7. A method of predistorting an RF signal to compensate for nonlinearities introduced when the RF signal is communicated, the method comprising the steps of:

(a) transmitting an RF signal from a first transmitter/receiver to a second transmitter/receiver on a first frequency;

(b) extracting nonlinearity data from the RF signal received at the second transmitter/receiver;

(c) transmitting a further RF signal containing the nonlinearity data from the second transmitter/receiver to the first transmitter/receiver on a second frequency; and

(d) predistorting RF signals to be transmitted from the first transmitter/receiver on the first frequency by using the received nonlinearity data;

(e) extracting further nonlinearity data from the further RF signal received at the first transmitter/receiver;

(f) transmitting the further nonlinearity data from the first transmitter/receiver to the second transmitter/receiver on the first frequency; and

(g) predistorting RF signals to be transmitted from the second transmitter/receiver on the second frequency by applying the received further nonlinearity data thereto.

8. A method of predistorting an RF signal to compensate for nonlinearities introduced when the RF signal is communicated, the method comprising the steps of:

(a) transmitting an RF signal from a first transmitter/receiver to a second transmitter/receiver on a first frequency;

(b) extracting nonlinearity data from the RF signal received at the second transmitter/receiver;

(c) transmitting a further RF signal containing the nonlinearity data from the second transmitter/receiver to the first transmitter/receiver on a second frequency; and

(d) predistorting RF signals to be transmitted from the first transmitter/receiver on the first frequency by using the received nonlinearity data, said predistorting comprising the steps of receiving the nonlinearity data at a receiver unit and providing the nonlinearity data to a predistorter in a transmitter unit through a reverse channel connection between the receiver and transmitter units.

9. A method of predistorting an RF signal to compensate for nonlinearities introduced when the RF signal is communicated, the method comprising the steps of:

(a) transmitting an RF signal from a first transmitter/receiver to a second transmitter/receiver;

(b) extracting nonlinearity data from the RF signal received at the second transmitter/receiver by the steps of,

(i) defining the nonlinearity data as constellation points related to data bits in the received RF signal,

(ii) defining an area for the constellation points that indicates when a nonlinearity has occurred, and

(iii) detecting when the constellation points fall into the defined area;

(c) transmitting a further RF signal containing the nonlinearity data from the second transmitter/receiver to the first transmitter/receiver; and

(d) predistorting RF signals to be transmitted from the first transmitter/receiver responsive to the received nonlinearity data.

10. The method of claim 9 wherein the constellation points are in an 2^N -QAM constellation, where N is an integer from four to eight.

11. The method of claim 10 wherein the data bits to which the constellation points are related include the two bits immediately following a least significant bit of a package of data in the received RF signal.

12. The method of claim 9 wherein the RF signal is transmitted on a first frequency and the further RF signal is transmitted on a second frequency.

13. A method of predistorting an RF signal to compensate for nonlinearities introduced when the RF signal is communicated, the method comprising the steps of:

(a) transmitting an RF signal from a first transmitter/receiver to a second transmitter/receiver on a first frequency;

(b) extracting nonlinearity data from the RF signal received at the second transmitter/receiver, the nonlinearity data including a count of a number of nonlinearities and nonlinearity corrections;

(c) communicating the nonlinearity data from a receiver unit in the second transmitter/receiver to a transmitter unit in the second transmitter/receiver through a reverse channel connection between the receiver and transmitter units;

(d) transmitting a further RF signal containing the nonlinearity data from the transmitter unit to the first transmitter/receiver on a second frequency; and

(e) communicating the nonlinearity data from a further receiver unit in the first transmitter/receiver to a further transmitter unit in the first transmitter/receiver through a reverse channel connection between the further receiver and transmitter units;

(f) predistorting RF signals to be transmitted from the further transmitter unit on the first frequency by using the received nonlinearity data.

14. The method of claim 13 wherein the step of extracting nonlinearity data comprises the steps of;

defining the nonlinearity data as constellation points;

defining an area for the constellation points that indicates when a nonlinearity has occurred; and

detecting when the constellation points fall into the defined area to provide the count of nonlinearities.

15. The method of claim 14 wherein the step of predistorting RF signals further comprises the steps of:

storing plural of the predistortion corrections that have been applied to RF signals and a corresponding count resulting therefrom; and

applying to RF signals to be transmitted a one of the plural predistortion corrections that provides an acceptable count.

16. A signal transmission system for predistorting a signal to compensate for nonlinearities in the communicated signal, the system comprising a processor for evaluating whether an output signal includes nonlinearities without reference to an input signal from which the output signal was derived, and a predistorter for applying results from said processor to a further input signal.

17. The system of claim 16 wherein said processor comprises means for identifying a nonrandom distribution of data in the output signal, the nonrandom distribution being indicative of a nonlinearity.

18. The system of claim 17 wherein the output signal comprises data bits and selected ones of the data bits define a constellation point, and further comprising means for determining whether a constellation point is in an area associated with random distribution of constellation points.

19. A signal transmission system for predistorting a signal to compensate for nonlinearities in the communicated signal, the system comprising plural transmitter/receivers, each of which comprises a transmitter unit and a receiver unit:

said transmitter unit comprising, a multiplexer for accepting input signals and for receiving nonlinearity information in a reverse channel connected to said receiver unit,

a predistorter for applying the nonlinearity information to the input signals,

an interpreter for receiving the nonlinearity information from said receiver unit and providing it in useable form to said predistorter, and

a transmitter for transmitting the input signals on a first frequency and for transmitting the nonlinearity information on a second frequency; and

said receiver unit comprising,

a receiver for receiving the input signals on the first frequency and for receiving the nonlinearity information on the second frequency,

a demodulator with a processor for extracting the nonlinearity information from the received input signals,

a controller unit for providing the nonlinearity information from said demodulator through said reverse channel to said multiplexer for transmission by said transmitter on the second frequency and to said interpreter for application in said predistorter.

20. The system of claim 19 wherein said processor comprises a counter for counting occurrences of nonlinearities in the received input signals, and means for generating a nonlinearity correction, and wherein the nonlinearity information includes the count and the nonlinearity correction.

21. A method of predistorting an RF signal to compensate for nonlinearities introduced when the RF signal is communicated, the method comprising the steps of:

(a) transmitting an RF signal from a first transmitter/receiver to a second transmitter/receiver on a first frequency;

(b) extracting nonlinearity data from the RF signal received at the second transmitter/receiver, said extracting performed in a receiver unit;

(c) transmitting a further RF signal containing the nonlinearity data from the second transmitter/receiver to the first transmitter/receiver on a second frequency, said transmitting performed in a transmitter unit;

(d) communicating the nonlinearity data from the receiver unit to the transmitter unit through a reverse channel connection between the receiver and transmitter units; and

(e) predistorting RF signals to be transmitted from the first transmitter/receiver on the first frequency by using the received nonlinearity data.