Pulse or digital communications – Transmitters – Angle modulation
Reexamination Certificate
1999-12-22
2002-05-14
Ghebretinsae, Temesghen (Department: 2631)
Pulse or digital communications
Transmitters
Angle modulation
C375S279000, C332S103000
Reexamination Certificate
active
06389081
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a signal transmission equipment which modulates and transmits signals accompanying clock information, such as the signals of the DS-Link (Distributed System-Link) system which is used the IEEE 1394 standard, for example.
2. Description of Related Art
In digital data transmission, it is necessary to transmit not only data signals but also clock signals for indicating timing to judge the data. To transmit clock signals, there is a method to transmit clock signals from the transmission side to the receive side along with data signals, and a method to generate clock signals at the receive side.
The DS-Link system is a method of transmitting clock signals from the transmission side to the receive side along with data signals. In the DS-Link system, two signals, that is, a data signal and strobe signal, are transmitted in parallel. To transmit such signals via radio transmission, signals must be modulated. For the modulation method, multi-value modulation, which transmits 2-bit information in one time slot (unit time), such as QPSK (Quadrature Phase Shift Keying) and 4-value FM, is usually used.
Another known method is to execute parallel/serial conversion so as to convert two signals to one signal, after which the signal is then transmitted.
Document 1 (“TDMA TSUSHIN”, pp. 85-87, Apr. 5, 1989, issued by IEICE) disclosed a method of transmitting only data signals using multi-value modulation, and generating clock signals from data signals at the receive side. Such a method is generally used in radio transmission.
To execute the above mentioned multi-value modulation, either amplitude modulation, frequency modulation or phase modulation is used. Normally phase modulation is more frequently used since the deterioration of signals due to the influence of fading is large in amplitude modulation, and circuits become complicated if frequency modulation is used. In phase modulation, however, the positions of signal points (phase status) in a phase diagram (called a constellation) may shift, crossing the origin of the phase diagram as signals change. In a phase diagram, as
FIG. 5
shows, the same phase of the carrier wave is mapped on the true axis (Ich), and the opposite phase of the carrier wave is mapped on the false axis (Qch). In the phase diagram, signal points (
0
,
0
), (
0
,
1
) (
1
,
1
) and (
1
,
0
) are positioned on the first to fourth quadrant respectively in this sequence, and the arrows in the phase diagram show the change of the signal points when the content of the signal changes. In the phase diagram, the distance between a signal point and the origin corresponds to the amplitude (power) of the signal. If a signal point shifts, crossing the origin in the phase diagram when the signal changes, this means that the signal has changed from a high amplitude status to a low amplitude status near the origin then back to a high amplitude status. Therefore, in order to accurately transmit this change of the amplitude between the transmitter and receiver, linear characteristics are demanded for both the transmitter and receiver. However, as Document 2 (“KIHON DENSHI KAIRO”, pp. 87-96, Jan. 10, 1984, issued by the Institute of Electrical Engineers) states, a linear amplifier (class A amplifier) has poor power efficiency.
Also in the case of the method of executing parallel/serial conversion, data signals and strobe signals are actually superimposed for transmission, therefore two times the transmission speed is required. This also makes it necessary to double the width of the frequency band.
In the case of the method for generating clock signals at the receive side, on the other hand, a clock generation circuit is necessary. Also a portion called the “preamble”, which is sufficient for the clock signal lead-in-time, must be added at the beginning of the transmission signal, which deteriorates the transmission efficiency. Especially when transmitting short burst signals at high-speed, the deterioration of transmission efficiency due to a preamble is a problem which cannot be ignored.
SUMMARY OF THE INVENTION
With the foregoing in view, it is an object of the present invention to provide a signal transmission equipment whereby good transmission quality can be obtained even if the linear characteristics of the transmitter/receiver are insufficient.
To achieve this object, the signal transmission equipment of the present invention has the following unique configuration. That is, the signal transmission equipment of the present invention comprises a transmitter and receiver. According to the present invention, the transmitter comprises a QPSK modulator. Also, according to the present invention, the QPSK modulator generates a modulation signal, including 2-bit digital information per unit time, which is formed based upon a first and second signal to be input. The modulation signal is output from the QPSK modulator. Also, according to the present invention, the receiver comprises a QPSK demodulator and an exclusive-or circuit. Also, according to the present invention, the QPSK demodulator converts the modulation signal sent from the transmitter to the first and second signals, and outputs therefrom the first and second signals. Also, according to the present invention, the exclusive-or circuit outputs a third signal, which is an exclusive-or of the first and second signals sent from the QPSK demodulator.
According to a preferred embodiment of the present invention, a change of the digital information which the first signal has, and a change of the digital information which the second signal has, occurs non-simultaneously.
For the embodiment of the present invention, it is preferable that the first signal is a data signal and the third signal is a clock signal.
According to another preferred embodiment of the present invention, the modulation signal is transmitted from the transmitter to the receiver by being irradiated into the air as electromagnetic waves.
According to still another preferred embodiment of the present invention, the modulation signal is transmitted from the transmitter to the receiver via optical fibers.
Another signal transmission equipment of the present invention has the following unique configuration. That is, the signal transmission equipment of the present invention comprises a transmitter and a receiver. According to the present invention, the transmitter comprises a QPSK modulator. Also, according to the present invention, the QPSK modulator generates a modulation signal, including 2-bit digital information per unit time, which is formed based upon a first and second signal to be input. The modulation signal is output from the QPSK modulator. Also, according to the present invention, the receiver comprises a QPSK demodulator. Also, according to the present invention, the QPSK demodulator converts the modulation signal, which is sent from the transmitter, to the first and second signals and outputs therefrom the first and second signals. Also, according to the present invention, in the QPSK modulator and QPSK demodulator, signal points (
0
,
0
), (
0
,
1
), (
1
,
0
) and (
1
,
1
) are positioned from the first quadrant to the fourth quadrant sequentially as binary numbers in a phase diagram, where the abscissa denotes a level of the first signal and the ordinate denotes a level of the second signal.
According to a preferred embodiment of the present invention, the first signal is a data signal and the second signal is a clock signal.
According to another preferred embodiment of the present invention, the modulation signal is transmitted from the transmitter to the receiver by being irradiated into the air as electromagnetic waves.
According to still another preferred embodiment of the present invention, the modulation signal is transmitted from the transmitter to the receiver via optical fibers.
Another signal transmission equipment of the present invention has the following unique configuration. That is, a signal transmission equipment of the present invention comprise
Kawakami Eiichiro
Shimizu Satoru
Sugitani Atsuhiko
Tokuda Kiyohito
Ghebretinsae Temesghen
Oki Electric Industry CO Ltd.
Rabin & Berdo P.C.
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