Distortion tolerant linear phase modulations

• US 20050078767A1
• Filed: 10/08/2003
• Published: 04/14/2005
• Est. Priority Date: 10/08/2003
• Status: Active Grant

• Current Assignee: Qingchong Liu
• Original Assignee: Qingchong Liu
• Inventors: Liu, Qingchong
• Granted Patent: US 7,558,333 B2
• Time in Patent Office: Days
• 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 signal and information transmission system and a method for communications or radar overcoming the distortion that can be caused by RF circuits including any of power amplifiers or up-converters or mixers or by the channel, the system comprising:

means for using error correcting codes to combat both the distortion caused by either RF circuits including power amplifiers and up-converters and mixers or the channel and the noise at the same time;

means for constructing phase modulated signals which can tolerate the distortion caused by the saturation of power amplifiers or the distortion caused by RF circuits such as up-converters and mixers or the channel;

means for minimizing the distortion caused by saturated power amplifiers and RF circuits to phase-shift-keyed signals at the output of one saturated power amplifier or many saturated power amplifiers or RF circuit;

means for employing any of class-C, class-D, class-E, or class-F power amplifiers, or class-A, class-B, class-AB power amplifiers working in the saturated region for signal power amplification or transmission;

means for simplifying the processes of design, development and manufacturing of power amplifiers, up-converters, mixers, RF circuits, radio terminals, communications terminals and radar;

means for reducing the radio cost, power amplifier cost, up-converter cost, mixer cost and terminal cost;

means for increasing the reliability of power amplifiers and RF circuits and the reliability of radio terminals;

means for achieving high spectral efficiency in the presence of distortion caused by power amplifiers, up-converters, mixers and RF circuits;

means for simplifying the terminal design, development and manufacturing;

means for increasing the battery life for communication terminals operated on battery;

means for filtering the received signal with distortion and noise by filters that are matched to the filters in the transmitter;

means for detecting the received signal;

means for estimating parameters in the received signal;

means for tracking the received signal in the presence of distortion and noise;

means for demodulating the received signal using the error correcting codes; and

means for achieving the bit error rate performance which is almost the same as the ideal linear BPSK bit error rate when any of class-F, class-E, class-D and class-C power amplifiers, or any of class-A, class-B, class-AB power amplifiers working in the saturated region is employed.

2. A system as recited in claim 1, comprising the encoder for error correcting codes to add redundancy to the information bits by applying turbo code, convolutional code, block code, or low density parity check code to combat the distortion caused by power amplifiers and RF circuits or the channel and to overcome the noise in the channel.

3. A system as recited in claim 1, comprising the modulator to take the input data stream and map the input data to the corresponding phase using the Gray coding for M-ary phase shift keying, M>

=2, and variations of phase shift keying.

4. A system as recited in claim 3, wherein said modulator constructs the modulated waveforms in orthogonal channels using finite impulse response filters.

5. A system as recited in claim 4, wherein said modulator uses pulse shaping functions including but not limited to the square-root raised cosine function, raised cosine function, and functions of Hanning, Hamming and Blackman.

6. A system as recited in claim 5, wherein said modulator constructs the linearly modulated waveforms of phase shift keying which do not have constant envelope in orthogonal channels.

7. A system as recited in claim 6, wherein said modulator generates waveforms to minimize the distortion after being amplified by power amplifiers of class-F, class-E, class-D, class-C, or power amplifiers of class-A, class-B, class-AB working in the saturation region.

8. A system as recited in claim 6, wherein said modulator constructs waveforms to minimize the distortion after being transmitted through the channel.

9. A system as recited in claim 1, comprising up-converters and power amplifiers to convert the baseband signal to the signal centered at the carrier frequency and amplify the signal.

10. A system as recited in claim 9, wherein said power amplifiers are class-F, class-E, class-D, class-C, or class-A, class-B, class-AB working in the saturation region, for high DC-to-AC power conversion efficiency.

11. A system as recited in claim 1, comprising an antenna or multiple antenna for transmission and reception of the signal.

12. A system as recited in claim 1, comprising a down-converter to convert the received signal to baseband.

13. A system as recited in claim 1, comprising the sampling circuit to sample the received signal.

14. A system as recited in claim 1, comprising filters in the receiver which are matched to the shaping filters in the transmitter or to the convolution of the impulses response functions of the shaping filter and the power amplifiers and the RF circuits in the transmitter.

15. A system as recited in claim 1, comprising correlators to correlate the received signal in orthogonal channels with the prestored waveforms or signals.

16. A system as recited in claim 1, comprising a signal detector which uses the output signals of the correlators to detect the signal or packet.

17. A system as recited in claim 1, comprising parameter estimators to estimate the carrier frequency, phase and symbol timing, using the output of correlators.

18. A system as recited in claim 1, comprising a tracking loop which uses the estimated carrier frequency, phase and symbol timing in the initialization of the loop to track the signal.

19. A system as recited in claim 1, comprising a decoder which can be the iterative decoder, the maximum likelihood decoder or the block decoder.

20. A system as recited in claim 19, wherein said decoder overcomes the distortion caused by power amplifiers or up-converters or RF circuits in the transmitter or by the channel and combats the noise in the channel, the decoding algorithm is optimal to the noise distribution.

21. A system as recited in claim 1, comprising a decoder which can achieve optimal or near optimal bit error rate performance in the presence of both distortion caused by RF circuits including the power amplifiers and the up-converters and mixers or by the channel, and noise such as AWGN.

22. A method of minimizing the distortion caused by at least one saturated power amplifier or up-converter or RF circuit to phase modulated signals, the method comprising of 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 the 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 the filtered in-phase signal; and

feeding the 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 the filtered quadrature signal.

23. Two pulse shaping filters as recited in claim 22, the first pulse shaping filter to filter the in-phase signal and the second pulse shaping filter to filter the quadrature signal, with the impulse response function p(t) of L≧

2 symbols long, and the pulse shaping function is preferred to satisfy;

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

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

t), T, is the symbol time;

when the impulse response p, (t) of the saturated radio or the channel is known to the designer, 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).

24. Two pulse shaping filters as recited in claim 22, the impulse response function of each filter is any of the square-root raised cosine function with the roll-off factor β

close to 1.0, the window functions of Hanning, Hamming, and Blackman, or any function satisfying the condition in claim 23.

25. A modulator implementing phase shift keying as recited in claim 22, the envelope of the modulated signal is not constant.

26. A method of achieving high spectral efficiency through proper pulse shaping in the presence of distortion caused by RF circuits including any of saturated power amplifier or up-converter or mixer or RF circuit for communications systems or radar employing phase shift keying.

27. A linear demodulator to demodulate the received signal in the presence of both distortion and noise, the linear 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.

28. A method of simplifying the design, development, manufacturing and testing of power amplifiers, up-converters, mixers, RF circuits, radio terminals and communications terminals for communications systems or radar employing phase shift keying.

29. A method of increasing the reliability of power amplifiers, RF circuits, radio terminals and communications terminals for communications systems or radar employing phase shift keying.

30. A method of reducing the power amplifier cost, up-converter cost, radio cost and terminal cost for communications systems or radar employing phase shift keying.

31. A method of increasing the battery life for communications terminals operated on battery.

32. A method of reducing the power consumption in transmitters for communications systems or radar employing phase shift keying.