# US 9,438,455 B2 · Modulation of signals

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- Number: US 9,438,455 B2
- Document ID: US9438455B2
- Status: Granted
- Kind: B2
- Application number: 13/697,442
- Filed: 2011-05-11
- Published: 2015-11-05
- Granted: 2016-09-06
- Earliest claimed: 2010-05-12
- Assignees: University of Pretoria
- Applicants: Kahesh Dhuness; Bodhaswar Tikanath Jugpershad Maharaj
- Inventors: Kahesh Dhuness; Bodhaswar Tikanath Jugpershad Maharaj
- Web page: https://patentgrep.com/patent/US9438455B2

## CPC

- H04L 27/18: Phase-modulated carrier systems, i.e. using phase-shift keying (H04L27/32 takes precedence)
- H04L 5/0007: {the frequencies being orthogonal, e.g. OFDM(A) or DMT}
- H04L 27/2614: {Peak power aspects}
- H04L 27/2634: {Inverse fast Fourier transform [IFFT] or inverse discrete Fourier transform [IDFT] modulators in combination with other circuits for modulation}
- H04L 27/26524: {Fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators in combination with other circuits for demodulation}
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

An orthogonal frequency division multiplexing (OFDM) modulation method, which includes phase modulating both the real and imaginary components of an OFDM signal.

## Claims

### Claim 1

A method of controlling peak to average power ratio (PAPR) of an orthogonal frequency divisional multiplexing (OFDM) signal, comprising:
with a serial to parallel converter of an OFDM modulator, separating an input OFDM signal into real and imaginary components;
with the OFDM modulator, scaling the real and imaginary components of the input OFDM signal to produce scaled real and scaled imaginary components of the input OFDM signal;
with the OFDM modulator, adding an offset term to the scaled real component of the input OFDM signal to produce an adapted real component of the input OFDM signal;
with the OFDM modulator, phase modulating the adapted real component and the scaled imaginary component to produce a phase modulated OFDM signal including a phase modulated real component and a phase modulated imaginary component; and
with the OFDM modulator, subtracting a dominant frequency component of the phase modulated OFDM signal from the phase modulated OFDM signal to produce an output signal with a controlled PAPR for transmission;
wherein:
the offset term impacts a value of the dominant frequency component.

### Claim 2 (depends on 1)

The method of claim 1, wherein the scaled real and scaled imaginary components of the input OFDM signal are represented by the following expressions, respectively:
Φ
1
⁡
(
t
)
=
⁢
(
m
⁡
(
t
)
)
ϛ
;
and
⁢
⁢
Φ
2
⁡
(
t
)
=
⁢
(
m
⁡
(
t
)
)
ϛ
in which (Φ1(t)) is the scaled real component, (Φ2(t)) is the scaled imaginary component, and are the real and imaginary components of the input OFDM signal, m(t) is an N-point inverse Fourier transform function, and ζ is a constant non-zero division term.

### Claim 3 (depends on 1)

The method of claim 1, further comprising, performing an inverse fast fourier transform (IFFT) operation with said OFDM modulator to produce said input OFDM signal.

### Claim 4 (depends on 1)

The method of claim 1, further comprising:
subtracting the phase modulated imaginary component from the phase modulated real component prior to subtracting said dominant frequency component.

### Claim 5 (depends on 4)

The method of claim 4, wherein:
the expression:
cos(2πfct+Φ1(t)+Ψos)−cos(2πfct+Φ2(t))
represents the addition of said offset term to the scaled real component and the subtraction of the phase modulated imaginary component from the phase modulated real component; and
wherein Φ1(t) and Φ2(t) represent the scaled real component and scaled imaginary components, respectively, Ψos represents said offset term, t is time, and fc represents the carrier frequency.

### Claim 6 (depends on 5)

The method of claim 5, wherein Ψos is at least twenty two times larger than Φ1(t) and Φ2(t).

### Claim 7 (depends on 5)

The method of claim 5, wherein:
γ2
⁢
⁢
J
0
⁡
(
β
)
2
⁢
sin
⁡
(
2
⁢
π
⁢
⁢
f
c
⁢
t
-
Ψ
OS
2
)
,
0
≤
γ
<
1
represents the dominant frequency component, in which γ is a dominant frequency component control factor, β is an adapted phase deviation of the real component and imaginary component of the input OFDM signal, and J0(β) is a Bessel function of the first kind of order 0 and argument β.

### Claim 8 (depends on 7)

The method of claim 7, further comprising,
with the OFDM modulator, adjusting γ to a value between 0 and 1.0.

### Claim 9

A method of demodulating an orthogonal frequency-division multiplexing (OFDM) signal, comprising, with an OFDM demodulator:
receiving an input modulated signal;
detecting a peak to average power ratio (PAPR) of the input modulated signal;
determining a predefined dominant frequency component control factor and a constant division term of the input modulated signal at least in part by examining the detected PAPR of the input modulated signal;
adding the predefined dominant frequency component to the input modulated signal to produce an input OFDM modulated signal; and
demodulating the input OFDM modulated input signal.

### Claim 10 (depends on 9)

The method of claim 9, further comprising, with said OFDM demodulator:
performing a fast Fourier transform (FFT) on the input OFDM modulated signal.

### Claim 11 (depends on 10)

The method of claim 10, further comprising passing the input OFDM modulated signal through an equalizer.

### Claim 12 (depends on 9)

The method of claim 9, wherein said OFDM demodulator determines said dominant frequency component control factor at least in part by accessing a lookup table that correlates PAPR to a plurality of predefined dominant frequency component control factor values, (γ), an offset term (Ψos) and the constant division term (ζ).

### Claim 13

An Orthogonal Frequency-Division Multiplexing (OFDM) modulator for controlling a peak to average power ratio (PAPR) of an OFDM transmission, comprising:
a multiplier configured to scale imaginary and real components of a transformed OFDM input signal to produce a scaled real component and a scaled imaginary component;
an offset term adder configured to add an offset term to the scaled real component of the transformed OFDM input signal, so as to produce an adapted real component;
a phase modulator configured to phase modulate the adapted real component and the scaled imaginary component of the transformed OFDM input signal using a cosinusoidal to produce a phase modulated OFDM signal including a phase modulated OFDM imaginary component and a phase modulated OFDM adapted real component;
a subtractor configured to subtract the phase modulated OFDM imaginary component from the phase modulated OFDM adapted real component; and
a subtractor configured to subtract a predefined dominant frequency from the phase modulated OFDM signal to produce an output signal with a controlled PAPR for transmission.

### Claim 14

An Orthogonal Frequency-Division Multiplexing (OFDM) demodulator, comprising:
a Peak-to-Average Power Ratio (PAPR) detector configured to determine a PAPR of an input modulated signal;
a memory comprising a lookup table referencing the PAPR against predefined values for a dominant frequency component control factor (γ), an offset term (Ψos), and a constant division term (ζ);
a processor configured to determine a predefined dominant frequency component control factor value associated with said input modulated signal from the predefined values in the lookup table;
an adder configured to add the predefined dominant frequency component control factor value to the input modulated signal to produce an input OFDM modulated signal; and
an OFDM demodulator configured to demodulate the input OFDM modulated signal.