Pulse or digital communications – Systems using alternating or pulsating current – Angle modulation
Reexamination Certificate
1997-10-23
2001-08-28
Pham, Chi (Department: 2631)
Pulse or digital communications
Systems using alternating or pulsating current
Angle modulation
C375S303000
Reexamination Certificate
active
06282246
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to frequency modulation methods and modem units, and more particularly to a frequency modulation method which carries out a frequency modulation using a common filter with respect to a mode which uses a large number of carrier frequencies, and to a modem unit which employs such a frequency modulation method.
2. Description of the Prior Art
Conventionally, various kinds of modem units which employ the frequency modulation technique have been proposed. When using a plurality of carrier frequencies, a modem unit on the transmitting end must be provided with a filter for each of the carrier frequencies. On the other hand, a modem unit on the receiving end must be provided with bandpass filters having passbands for passing the frequencies corresponding to the original binary data values. The original binary data values are judged depending on the existence of outputs of the bandpass filters.
However, when a number of filters corresponding to the plurality of carrier frequencies are provided, the load on the modem design increases, and there were problems in that the construction of the modem unit becomes complex and the modem unit cannot be manufactured at low cost.
On the other hand, in order to judge the data by a digital signal processing by subjecting the received data to an analog-to-digital conversion, it is necessary to use a bandpass filter having a narrow band. But in order to realize the bandpass filter having the narrow band, it is inevitably necessary to set the number of taps of the bandpass filter to a large value, so as to satisfy a sufficient blocking characteristic. As a result, there were also problems in that the amount of computation processes and delays in the bandpass filter become large, and that it is difficult to improve the performance of the modem unit.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a frequency modulation method which can suppress the increase of the delays by using a simple and inexpensive structure and making the amount of signal processing relatively small, and to provide a modem unit employing such a frequency modulation method.
This and other objects of the present invention are attained by a frequency modulation method comprising a frequency-shifting step for subjecting an input data to a frequency shift corresponding to a binary data value; a filtering step for filtering an output obtained by said frequency-shifting step so as to limit said output to a common band; and a modulation step for frequency-modulating an output obtained by said filtering step by a carrier frequency having an intermediate value of the frequencies respectively corresponding to the binary data values (“1” and “0” and defined by FSK modulation).
In the frequency modulation method of the present invention, the input data may be subjected in the frequency-shifting step to the frequency shift with a frequency shifting quantity corresponding to the maximum data transmission rate.
An unwanted band may be limited in the filtering step corresponding to a data transmission rate.
The frequency modulation method of the present invention may further comprise a step for limiting the input data within a frequency band of a transmission medium through which frequency modulated data obtained by the modulation step is transmitted, before the frequency-shifting step.
The frequency modulation method of the present invention may further comprise a step for automatically setting parameters used in at least the frequency-shifting step and the filtering step depending on a data transmission rate.
The objects of the present invention are also attained by a modem unit comprising frequency-shifting means for subjecting an input data to a frequency shift corresponding to a binary data value; filtering means for limiting an output obtained by said frequency-shifting means to a common band; and modulation means for frequency-modulating an output value obtained by said filtering means by a carrier frequency having an intermediate value of the frequencies respectively corresponding to the binary data values (“1” and “0” and defined by FSK modulation).
The frequency-shifting means may subject the input data to the frequency shift with a frequency shift quantity corresponding to a frequency difference of corresponding binary data values.
In the modem unit of the present invention, the filtering means may limit an unwanted band corresponding to a data transmission rate.
The modem unit of the present invention may further comprise means for limiting the input data within a frequency band of a transmission medium through which frequency modulated data obtained by the modulation means is transmitted, at a stage before the frequency-shifting means.
According to the invention, the modem unit may further comprise means for automatically setting parameters used in at least the frequency-shifting means and the filtering means depending on a data transmission rate.
The objects of the present invention can also be realized by a modem unit comprising demodulation means for demodulating a frequency modulated data, which is obtained by frequency-modulating an input data, by a carrier frequency having an intermediate value of the frequencies respectively corresponding to the binary data values; means for obtaining a phase shift quantity from a phase difference of vector signals of a baseband obtained from said demodulation means; and judging means for judging a binary data value from the input data based on the phase shift quantity obtained by said means for obtaining a phase shift quantity.
According to the present invention, the means for obtaining a phase shift quantity may include means for normalizing the vector signals of the baseband obtained from the demodulation means.
According to the present invention, the judging means of the modem unit may include first means for judging the binary data value of said input data based on a polarity of the phase shift quantity.
The judging means of the modem unit may further include second means for holding a judgement result of the binary data value corresponding to the polarity for a predetermined holding time after said first means judges the polarity of the phase shift quantity.
According to the present invention, the modem unit may further comprise means for holding the binary data value when the carrier is OFF.
The construction of a transmitting system of the modem unit of the present invention is simple and the modem unit can be manufactured at low cost, because a common band limiting operation is carried out by common filter means even if a large number of carrier frequencies are used.
The frequency-shifting means may be a circuit which subjects the input data to the frequency shift and has a relatively simple construction, and the amount of computation processes carried out is relatively small.
It is possible to use a common filter means with respect to each carrier to suit the data transmission rate.
It is also possible to carry out an optimum signal processing with respect to the transmission medium used for the data transmission in the step for limiting the input data within a frequency band of a transmission medium through which frequency obtained by the modulation step is transmitted, before the frequency-shifting step.
It is possible to carry out the frequency modulation to suit the data transmission rate using the same circuit construction due to automatically setting parameters used in at least the frequency-shifting step and the filtering step depending on a data transmission rate.
The amount of signal processing in the receiving system is relatively small because the frequency change in the vector signal of the baseband obtained from the demodulation means is obtained from the phase shift quantity based on the phase difference. In addition, it is possible to accurately demodulate the frequency modulated data because the delay quantity does not become large.
By providing means for normalizing the vector sign
Kaku Takashi
Okita Ryoji
Fujitsu Limited
Helfgott & Karas P.C.
Pham Chi
Phu Phuong
LandOfFree
Frequency modulation method and modem unit employing such... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Frequency modulation method and modem unit employing such..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Frequency modulation method and modem unit employing such... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2485628