Waveform shaping method and equipment

Details Waveform shaping method and equipment Waveform shaping method and equipment

1998-05-18

2001-06-05

Vo, Don (Department: 2734)

Pulse or digital communications

Systems using alternating or pulsating current

C375S296000, C360S040000

Reexamination Certificate

active

06243422

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the waveform shaping equipment and waveform-shaping method for generating bandlimited signals, and for preventing band spread at the head and trail at the edge of burst when burst-like data string is transmitted in the data transmission in which data is transmitted in the form of packet.
2. Related Art of the Invention
In the radio communication, etc., when a packet comprising transmission data is transmitted, it is necessary to limit the bandwidth (bandlimitation) to prevent adjacent channel interference for effective utilization of frequency. For bandlimitation of signals, it is common to limit the bandwidth with respect to the signal waveform of the baseband. Two systems are available for band-limiting the baseband signal waveform: an analog system using analog filter and a digital system by digital signal processing. One of the digital systems is the method to shape waveform by reading out and concatenating the baseband signal waveform previously band-limited by calculation from the memory table such as ROM and the like (for example, IEEE transactions on Communications, COM-vol. 25, No. 10, Pages 1243-1244). When the waveform shaping method using this memory table system is used, the ideal filter frequency response can be more accurately realized than analog system waveform shaping method, and the shaped waveform can be changed only by rewriting the memory contents, achieving high versatility. It is also suited for the VLSI technique and can be comparatively downsized.
Referring now to the drawings, the conventional waveform shaping equipment using the above-mentioned method is described with special emphasis placed on the readout principle of shaped waveform and hardware configuration of the waveform shaping equipment.
FIG. 1
shows input data to the waveform shaping equipment. D(
1
), D(
2
) . . . , D(k), . . . D(n) show transmission data and X shows the data other than the transmission data,which does not have any information. Each data is successively read into the waveform shaping equipment at every time interval T.
FIG. 2
a
shows the data pattern comprising each input data of FIG.
1
. The data pattern is used to specify part of the address for reading out waveform after bandlimitation from the memory table. In this section, to simplify, description is made supposing that there is an intersymbol interference which has 3 symbols time and the data pattern length is 3 symbols. A(
1
), A(
2
), and A(
3
) show a time slot, respectively. Let the time slot A(
2
) in each data pattern be the present time slot. Then, time slots A(
1
), A(
3
) affect the present time slot A(
2
) by intersymbol interference. Each data pattern (p(
1
), p(
2
), p(
3
), p(
4
), data, respectively, and the data pattern p(
1
) comprises the data (D(
1
), X, X), the data pattern p(
2
) comprises the data (D(
2
), D(
1
), X), the data pattern p(
3
) comprises the data (D(
3
), D(
2
), D(
1
)), the data pattern p(
4
) comprises the data (D(
4
), D(
3
), D(
2
)), the data pattern p(n) comprises the data (D(n), D(n-
1
), D(n-
2
)), the data pattern p(n+
1
) comprises the data (X, D(n), D(n-
1
)), and the data pattern p(n+
2
) comprises the data (X, X, D(n)).
FIG. 3
shows the case when the data pattern corresponding to the present time slot which varies at every time interval T is extracted.
FIG. 2
b
shows baseband waveform after bandlimitation, which is generated when the waveform is read out from the memory table successively at every 1 symbol time T by the data pattern shown in FIG.
3
. That is, the waveform w(
3
) which has 1 symbol time is generated by the data pattern p(
3
), the waveform w(
4
) equivalent to 1 symbol time is generated by the data pattern p(
4
), and the waveform w(n) equivalent to 1 symbol time is generated by the data pattern p(n). Because in the data patterns p(l), p(
2
), p(n+
1
), and p(n+
2
) indefinite data X with no information is contained, it is designed to output the 0-level waveform as the waveform for w(
1
), w(
2
), w(n+
1
), and w(n+
2
) at the time corresponding to data patterns p(
1
), p(
2
), p(n+
1
), and p(n+
2
).
FIG. 4
shows one example of a block diagram showing the hardware configuration of conventional waveform shaping equipment. In
FIG. 4
, S
3
denotes a shift register, C
3
a counter, M
3
a memory table, D
3
a D/A converter, and L
3
a low-pass filter. dt
3
denotes a dta string, co
3
a counter output, so
3
a shift register output, mo
3
a memory output, wd
3
a continuous waveform after D/A conversion wl
3
a shaped waveform after smoothing. In general, let the data string dt
3
be the data string of 2{circumflex over ( )}M value (M: natural number), 1 symbol is M bits and the shift register
101
is made up of M bits×3 stages. Therefore, the output from each stage becomes M bit each, respectively. For simplification, description will be made assuming that the shift register handles M=1, that is,binary data.
The shift register S
3
accumulates data for latest 3 bits of the data string dt
3
, and while taking in 1-bit data from the data string dt
3
at every 1 symbol time and shifting, it outputs 3-bit data pattern so
3
in parallel. The memory table M
3
is a ROM which stores waveform data for one symbol time with the effects of intersymbol interference taken into account by prior calculation. That is, it stores waveform data for all the patterns which the total of 3 bits comprising the symbol to be transmitted and symbols before and after can take. Now, let the waveform data for one symbol time comprise 8 samples. The counter C
3
is a 3-bit counter, which counts up 8 times in one symbol time and repeats operation with one symbol time as one cycle. The memory table M
3
designates a total of 6 bits as an address, which comprises 3-bit data pattern so
3
, an output of each stage of the shift register S
3
, and 3-bit output co
3
of the counter C
3
which represents the location in one symbol time, retrieves the waveform data at each time corresponding to the data pattern to be transmitted, and outputs the memory output mo
3
. The memory output mo
3
is converted to continuous waveform wd
3
at the D/A converter D
3
and after smoothed at the lowpass filter L
3
, it become shaped waveform wl
3
.
Next discussion will be made on the method for generating baseband signals after bandlimitation in the QPSK using this method.
FIG. 5
a
shows data of the in-phase axis and quadrature axis extracted at every time slot from the transmission data string in the QPSK. Expressing this as a transition state for each time slot on the signal space produces FIG.
6
. In
FIG. 6
, each signal point transitions at each time slot and the locus on the time axis of the orthogonal projection cast on the in-phase axis and quadrature axis of the coordinates of transitioning signal point represents the baseband signal waveforms of the in-phase axis and quadrature axis.
FIG. 5
b
shows the baseband signal waveform of the in-phase axis and the quadrature axis corresponding to the in-phase axis and quadrature axis data shown in
FIG. 5
a
before bandlimitation. When the baseband signal waveform of the in-phase axis and quadrature axis shown in
FIG. 5
b
are band-limited with the intersymbol interference of the data pattern length taken into account, the baseband signal waveform after bandlimitation as shown in
FIG. 5
c
can be obtained. The in-phase axis signal waveform and the quadrature axis signal waveform make the H level of waveform correspond to the data value “
0
” and the L level of waveform to “1” as shown in
FIG. 5
b
and
5
c.
In the case of the QPSK, since the baseband signal waveform of the in-phase axis is determined by the in-phase component of the coordinates of each signal point and that of the quadrature axis by the quadrature component, the data patterns of the in-phase axis and the quadrature axis can be obtained separately from the in-phase component and the quadrature component in the time slot. In addition,

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