Pulse or digital communications – Transceivers
Reexamination Certificate
1999-09-30
2003-04-15
Ghayour, Mohammad H. (Department: 2734)
Pulse or digital communications
Transceivers
C375S260000, C370S203000, C370S210000
Reexamination Certificate
active
06549566
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wireless transceiver system using Multi Carrier modulation and, in particular, to a Multi Carrier transceiver which can reduce a transmission bandwidth to one half of required bandwidth by using a symmetry of discrete Fourier transformed signal and a method thereof.
2. Information Disclosure Statement
In general, a high speed wireless transmission mainly uses a Direct-Sequence Spectrum Spread Method, a frequency hopping method or a Multi Carrier transmission method.
With reference to
FIGS. 1 and 2
, a basic concept of multi carrier modulation method used in the multi carrier transmission method is described.
FIG. 1
illustrates a basic transmission structure of the multi carrier modulation method having N subcarriers.
The basic concept of the multi carrier modulation method is to transmit by dividing an available frequency into several subchannels. These subchannels orthogonally overlap each other.
When a symbol interval is taken as T, the interval &Dgr;f between the subcarriers which can assure the orthogonality is a multiple of k/T (k is an integer).
FIG. 2
shows a signal spectrum of multi carrier modulation method.
The system of
FIGS. 1 and 2
can be analyzed by an equation 1.
s
(
t
)
=
∑
k
=
0
n
-
1
X
k
cos
(
2
π
f
c
t
+
2
π
k
Δ
ft
)
=
∑
k
=
0
N
-
1
X
k
cos
2
π
f
c
t
cos
2
π
k
T
t
-
∑
k
=
0
N
-
1
X
k
sin
2
π
f
c
t
sin
2
π
k
T
t
=
m
l
(
t
)
cos
2
π
f
c
t
-
m
q
(
t
)
sin
2
π
f
c
t
m
l
(
t
)
=
∑
k
=
0
N
-
1
X
k
cos
2
π
k
T
t
m
q
(
t
)
=
∑
k
=
0
N
-
1
X
k
sin
2
π
k
T
t
[
Equation
1
]
In equation 1, it can be known that s(t) is in form obtained by modulating baseband signals m
I
(t) and m
g
(t) with a frequency fc. Defining t=nT/N in the baseband signals m
I
(t) and m
g
(t), a discrete signal form of the base band signals is obtained.
m
l
(
n
)
=
∑
k
=
0
N
-
1
X
k
cos
2
π
nk
N
m
q
(
n
)
=
∑
k
=
0
N
-
1
X
k
sin
2
π
nk
N
[
Equation
2
]
It can be seen that the equation 2 is a same representation as an N point Inverse Discrete Fourier Transform (IDFT) with the exception of a scaling factor 1/N and j of imaginary term. Therefore, the baseband signal can be implemented by carrying out the IDFT of a symbol to be transmitted, and the same result can be obtained by dividing the result of IDFT into real terms and imaginary terms, transforming the discrete signal into a continuous signal, modulating the result with the frequency fc and carrying out a sum operation thereof. At this time, it should be noted the (−) sign must be put in sum operation of imaginary parts. The Discrete Fourier Transform (DFT) block can be further fast calculated by using a fast Fourier transform (FFT) digital signal processor (DSP). A construction of a Multi Carrier wireless transceiver of Orthogonal Frequency Division Multiplexing (OFDM) method based on the FFT is shown in FIG.
3
.
FIG. 3
is an illustrative construction drawing of a conventional Multi Carrier wireless transceiver which comprises a serial/parallel (S/P) conversion section
111
, an Inverse Fast Fourier transformation section (IFFT)
112
, a parallel/serial (P/S) transformation section
113
, a digital/analog (D/A) conversion section
114
, a modulation section
115
, a phase shift section
116
, a synthesizing section
117
, a transceiving channel
118
, a demodulation section
119
, a phase shift section
120
, a low pass filter
121
, an analog/digital (A/D) conversion section
122
, a serial/parallel conversion section
123
, a Fast Fourier Transformation section (FFT)
124
and a parallel/serial conversion section
125
.
A description of operation of the conventional Multi Carrier wireless transceiver having a structure described above is given below.
The serial/parallel conversion section
111
converts the transmission data into N low speed parallel binary data and transmits the converted data to the IFFT section
112
.
The IFFT section
112
inverse Fourier transforms the input data by taking the input data as frequency domain spectrum components and transmits to the parallel/serial conversion section
113
an output composed of a real part data sequence and an imaginary part data sequence.
The parallel/serial conversion section
113
divides the Inverse Fourier transformed parallel data into a real part and imaginary part, inserts a guard bit for preventing an adjacent signal interference in a transmitting channel, converts the parallel data into a serial data sequence and transmits it to the digital/analog conversion section
114
. At this time, the output is divided into a real part (Re) data and imaginary part (Im) data. The digital/analog conversion section
114
converts an input Multi-level digital signal into analog signal and transmits the converted signal to the modulation section
115
. The modulation section
115
multiplies the input analog signals with a carrier of cos 2&pgr; f
c
t and a carrier obtained by shifting the phase of the former carrier by 90 degree by the phase shift section
116
, respectively. The synthesizing section
117
inverts the sign of the imaginary part signal from the modulation section
115
, adds the imaginary part signal to the real part signal, and transmits the added signal through the channel
118
.
The demodulation section
119
divides the received signal from the channel
118
, restores the divided signals to signals same as the output signals from the digital/analog conversion section
114
by multiplying the divided signals with a signal of cos 2&pgr; f
c
t having same frequency and phase as the carrier and a signal obtained by shifting the phase by 90 degree by the phase shift section
120
, respectively, and transmits them to low pass filters
121
. The low pass filters
121
only passes low frequency band among the demodulated signals, and the analog/digital conversion section
122
converts the analog signal transmitted from the low pass filters
121
into digital and transmits it to the serial/parallel conversion section
123
.
The serial/parallel conversion section
123
converts the input real part signal and inverted imaginary part signal into N low speed parallel binary data, removes the guard bit and transmits the data to the FFT section
124
. The FFT section
124
discrete Fourier transforms the input discrete parallel data and transmits the data to the parallel/serial conversion section
125
, and the parallel/serial conversion section
125
converts the Fourier transformed parallel data into serial data stream.
FIG. 4
is a wireless channel frequency spectrum diagram in which the signal transmitted from the conventional Multi Carrier wireless transceiver is presented in a frequency spectrum at the channel.
As shown in
FIG. 4
, the conventional Multi Carrier wireless transceiver occupies a bandwidth of (N+1)&Dgr;f, where the &Dgr;f is the carrier interval.
As shown in
FIG. 4
, in case of using the conventional Multi Carrier wireless transceiver, since the occupied bandwidth at the wireless or wired channel is large, there are problems that degrades transmission efficiency and is vulnerable to multi-path fading, noise and interference.
Chung Hae Won
Kim Jong Ho
Lee Chan Goo
Lim Myoung Seob
Antonelli Terry Stout & Kraus LLP
Electronics and Telecommunications Research Institute
Ghayour Mohammad H.
LandOfFree
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