Distortion tolerant linear phase modulations

• US 7,558,333 B2
• Filed: 10/08/2003
• Issued: 07/07/2009
• Est. Priority Date: 10/08/2003
• Status: Active Grant

• Current Assignee: Qingchong Liu
• Original Assignee: Qingchong Liu
• Inventors: Liu, Qingchong
• Primary Examiner(s): Ghayour; Mohammad H
• Assistant Examiner(s): Panwalkar; Vineeta S
• Application Number:
  US10/681,846
• Publication Number:
  US 20050078767A1
• Time in Patent Office: 2,099 Days
• Field of Search: 375/295, 375/296, 375/302, 375/308, 375/309, 375/312, 375/316, 375322-326, 375/340, 375/341, 375/343, 375/346, 375/259, 375/260, 375/262, 375/265, 375/268, 375/269, 375/271, 375/279, 375/283, 455/91, 455/114.2, 455/114.3, 455/127.1, 455/127.2, 455/127.3, 455/127.5, 330/207.A, 330/207.R
• US Class Current: 375/297
• CPC Class Codes: H04L 27/18 Phase-modulated carrier systems, i.e. using phase-shift keying H04L27/32 takes precedence

Abstract

A signal and information transmission system for communications or radar and a method of achieving distortionless transmission of linear phase shift keying signals amplified by nonlinear power amplifiers or distorted by up-converters and RF circuits or the channel. Error correcting codes are used to jointly overcome both the distortion by the power amplifiers or up-converters and RF circuits or the channel and the noise. The modulator generates properly pulse shaped PSK signal, which does not have constant envelope. The signal-to-distortion power ratio is maximized to be above 20 dB at the fully saturated power amplifier output. The simplest linear receiver is provided to demodulate the received signal in the presence of radio distortion, channel distortion and noise. The decoder makes decision in the presence of radio distortion, channel distortion and noise. The method guarantees distortionless transmission of PSK signals for communications systems or radar employing power amplifiers of high DC-to-AC power conversion efficiency including class-F, class-E, class-D, class-C, or any of class-A, class-B, class-AB working in the saturation region. The method can achieve high bandwidth efficiency.

Claims

1. A method of minimizing the distortion caused by a saturated power amplifier or up-converter or RF circuit to phase modulated signals, the method comprising the steps of:

mapping k bits d=(d₁,d₂, . . . ,d_k) at a time to one of M=2^k phases, the mapped phase is φ

(d), which is a symbol;

feeding a coefficient cos φ

(d) to a first finite impulse response filter for summing a series of the delayed filter coefficients {p(j)} weighted by the symbol coefficients {cos φ

(d)} to form a filtered in-phase signal; and

feeding a coefficient sin φ

(d) to a second finite impulse response filter for summing a series of the delayed filter coefficients {p(j)} weighted by the symbol coefficients {sin φ

(d)}to form a filtered quadrature signal, wherein the filtering of the in-phase signal and the quadrature signal with a pulse shaping function p(t) of L≧

2 symbols long, and the pulse shaping function satisfies;

$x<br><br>\left(t={\mathrm{kT}}_s\right)=\{\begin{array}{cc}1& \mathrm{If}<br><br><br><br>k=L\\ 0& \mathrm{Else}\end{array}$

where x(t) is the convolution of p(t) and p(LT_s−

t), T_s is the symbol time;

when the impulse response p₁ (t) of the saturated power amplifier is known, the function x(t) is the convolution of g(t)=p(t)*p₁(t) and g(T−

t), where T is the duration of g(t).

2. The method as recited in claim 1, including the step of using a function in a class including a square-root raised cosine function with the roll-off factor β

in a range between 0.6 and 1.0, inclusive, a Hanning function, a Hamming function, and a Blackman function.

3. The method as recited in claim 2, wherein an envelope of the modulated signal varies.

4. The method as recited in claim 1 further including the step of minimizing power spectral sidelobe regrowth in the presence of distortion caused by RF circuits.

5. A communication system for transmitting and receiving an input data stream, said communication system comprising:

a transmitter for receiving the input data stream and transmitting the input data stream out therefrom, said transmitter including a modulator defining a pulse shaping function p(t) for mapping the input data stream using phase shift keying to create a modulated signal, and an amplifier working in a saturation region and defining an impulse response function p₁(t) for amplifying the modulated signal to create an amplified modulated signal, wherein said pulse shaping function and said impulse response function are convoluted such that the pulse shaping function and the impulse response function satisfy;

$\begin{array}{c}x<br><br>\left(t={\mathrm{kT}}_s\right)=<br><br>1,\mathrm{if}<br><br><br><br>k=L\\ =<br><br>0,\mathrm{Else}\end{array}$

where L is the number of symbols and T_s is the symbol time;

where x(t) is the convolution of g(t)=p(t)*p₁(t) and g(T−

t), where T is the duration of g(t);

a channel through which the amplified modulated signal is transmitted; and

a receiver to receive the amplified modulated signal to down convert the amplified signal to retrieve the input data stream therefrom.

6. The communication system as recited in claim 5 wherein said transmitter includes an encoder to reduce distortion caused by said power amplifier and said channel.

7. The communication system as recited in claim 5, wherein said modulator constructs the modulated signal in orthogonal channels using first and second finite impulse response filters.

8. The communication system as recited in claim 7, wherein said first and second finite impulse response filters apply pulse shaping functions to the input data stream to create the modulated signal.

9. The communication system as recited in claim 8, wherein said modulator constructs the modulated signal of phase shift keying having a variable envelope in the orthogonal channels.

10. The communication system as recited in claim 9 wherein said receiver includes filters matched to said first and second finite impulse response filters in said transmitter.

11. The communication system as recited in claim 8, wherein said first and second finite impulse response filters define a square root raised cosine function having a roll-off factor (β

) in a range between 0.6 and 1.0, inclusive.

12. The communication system as recited in claim 11 wherein said square root raised cosine function defines a duration of symbols (L) in the range between 2 and 6, inclusive.

13. The communication system as recited in claim 12 wherein said receiver includes correlators to correlate the amplified modulated signal in orthogonal channels with prestored waveforms or signals, said correlators create an output signal from the amplified modulated signal.

14. The communication system as recited in claim 13 wherein said receiver includes a signal detector to detect the input data stream from the output signal.

15. The communication system as recited in claim 14 including a parameter estimator to estimate carrier frequency, phase and symbol timing, using the output signal of said correlators.

16. The communication system as recited in claim 15 including a tracking loop which uses the carrier frequency, phase and symbol timing estimated by said parameter estimator to track the input data stream.

17. The communication system as recited in claim 16 wherein said receiver includes a decoder.

18. The communication system as recited in claim 17, wherein said decoder overcomes the distortion caused by said transmitter and said channel using a decoding algorithm is optimal to noise distribution.

19. The communication system as recited in claim 12, wherein said amplifier includes class-F, class-E, class-D, class-C amplifiers, and class-A, class-B, class-AB amplifiers working in the saturation region.

20. The communication system as recited in claim 5, comprising an antenna for transmission and reception of the amplified modulated signal.

21. The communication system as recited in claim 20 wherein said receiver includes a down-converter to convert the received signal to a baseband.

22. The communication system as recited in claim 21 wherein said receiver includes a sampling circuit to sample the amplified modulated signal.

23. The system as recited in claim 20 further comprising a demodulator to demodulate the amplified modulated signal in the presence of both distortion and noise, the demodulator comprising:

a first down-converter to convert the received signal in the in-phase channel to baseband;

a second down-converter to convert the received signal in the quadrature channel to baseband;

a sampling circuit to sample the baseband signals in both the in-phase channel and the quadrature channel;

an analog-to-digital converter to convert the sampled baseband signals to digital signals;

a first finite impulse response filter matched to the shaping filter for the in-phase channel in the transmitter, the filter performs low-pass filtering for the samples in the in-phase channel;

a second finite impulse response filter matched to the shaping filter for the quadrature channel in the transmitter, the filter performs low-pass filtering for the samples in the quadrature channel;

a signal detector to detect the incoming signal using the matched filter output;

a parameter estimator to estimate the symbol timing, carrier frequency offset and carrier phase using the matched filter output;

a tracking loop to track the carrier frequency, carrier phase and the symbol timing; and

a decoder to make decisions on the received symbols using the tracking loop output.

24. A transmitter for receiving an input data stream and transmitting the input data stream out therefrom, said transmitter comprising:

a modulator defining a pulse shaping function p(t) for mapping the input data stream using phase shift keying to create a modulated signal, said modulator including first and second finite impulse response filters to construct the modulated signal in orthogonal channels, wherein said first and second finite impulse response filters define a roll-off factor (β

) in a range between 0.6 and 1.0, inclusive, for a square root raised cosine function; and

an amplifier defining an impulse response function p₁(t) for amplifying the modulated signal to create an amplified modulated signal, wherein said pulse shaping function and said impulse response function are convoluted to minimize the effect of noise and distortion allowing the input data stream to be demodulated and read such that the pulse shaping function and the impulse response function satisfy;

$\begin{array}{c}x<br><br>\left(t={\mathrm{kT}}_s\right)=<br><br>1,\mathrm{if}<br><br><br><br>k=L\\ =<br><br>0,\mathrm{Else}\end{array}$

where L is the number of symbols and T_s is the symbol time;

where x(t) is the convolution of g(t)=p(t)*p₁(t) and g(T−

t), where T is the duration of g(t).

25. A method for phase shift keying communications systems for use with nonlinear power amplifiers and linear power amplifiers working in saturation region to achieve bit error performance compatible to bit error rate of phase shift keying communications system using linear power amplifier, the method comprising of the steps of:

generating a phase shift keying signal using square root raised cosine function with roll-off factor in a range between 0.6 and 1.0 as pulse shaping function p(t) to create a modulated signal;

amplifying the modulated signal to create an amplified modulated signal by a nonlinear power amplifier or a linear power amplifier working in saturation region with impulse response function p₁(t), the pulse shaping function and the impulse response function satisfying;

$x<br><br>\left(t={\mathrm{kT}}_s\right)=\{\begin{array}{cc}1& \mathrm{If}<br><br><br><br>k=L\\ 0& \mathrm{Else}\end{array}$

where L is the number of symbols and T_s is the symbol time; and

where the function x(t) is the convolution of g(t)=p(t)*p₁(t) and g(T−

t), where T is the duration of g(t);

filtering the modulated amplified signal in the in-phase channel by a finite impulse response filter matched to the convolution of the said pulse shaping function and the said impulse response function;

filtering the modulated amplified signal in the quadrature channel by a finite impulse response filter matched to the convolution of the said pulse shaping function and the said impulse response function; and

using the output signals of the said finite impulse response filters to retrieve the information data stream.