Pulse or digital communications – Pulse amplitude modulation
Reexamination Certificate
1998-07-21
2001-07-31
Chin, Stephen (Department: 2634)
Pulse or digital communications
Pulse amplitude modulation
C375S295000, C332S115000
Reexamination Certificate
active
06269134
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transmission method in a communication system employing pulse amplitude modulation (PAM) to decrease errors generated when converting digital signals into analog signals.
2. Discussion of Related Art
A pulse communication method refers to a communication method for transmitting information using a rectangular pulse string as a carrier, where differences in the amplitude, width, temporal position, and/or repetition of pulses in that rectangular pulse string represent signals to be transmitted. A pulse amplitude modulation (PAM) system represents information to be transmitted by changing the amplitude of pulses in the rectangular pulse string that is used as a carrier. Since pulse amplitude modulation (PAM) changes only the amplitude of pulses in the carrier, the temporal position of a pulse string and pulse width remain constant. Thus, the configurations of a modulator and demodulator in this system are simple. However, in such a system, noise at the input translates into noise at the output.
FIG. 1
is a block diagram of a transmitter for transmitting data in a conventional data transmit-receive device employing a PAM system. The transmitter largely consists of: digital circuit
100
for converting the information to be transmitted into binary data; and PAM modulator
200
for converting the binary data transmitted from digital circuit
100
into analog signals, and for modulating the analog signals before sending them to the predetermined channel
300
. PAM modulator
200
consists of: D/A converter
210
for converting binary data input thereto into analog signals; a filter
220
for eliminating frequencies of analog signals output that are outside from D/A converter
210
predetermined critical limits; and matching unit
230
for matching the signals output from filter
220
with the characteristics of channel
300
.
The operations of the conventional transmitter employing such the PAM system are as follows. Digital circuit
100
is used to convert information to be transmitted into digital information or binary data. PAM modulator
200
converts the binary data output from digital circuit
100
into analog signals according to a PAM system, and outputs those signals to channel
300
.
In PAM modulator
200
, D/A converter
210
converts the binary data received from digital circuit
100
into analog signals.
The signal output by D/A converter
210
is a sampling signal, Vak, corresponding to the binary data. Filter
220
eliminates frequencies that are outside predetermined critical limits from sampling signal Vak, effectively converting sampling signal Vak into a sinusoidal analog signal, Vfk. Since the sinusoidal analog signal Vfk generated by filter
220
does not match the characteristics of channel
300
, matching unit
230
converts sinusoidal analog signal Vfk into a matching signal, Vok, which matches the characteristics of channel
300
.
FIG. 2
is a waveform diagram illustrating a comparison between ideal and actual outputs of each component in the PAM modulator in response to a binary data output of 6 bits from digital circuit
100
, showing output signal properties of each component in the conventional transmitter employing the PAM system.
As shown in
FIG. 2
, when the binary data generated by digital circuit
100
is converted by PAM modulator
200
, the matching signal Vok generated by PAM modulator
200
becomes distorted since the properties of PAM modulator
200
are not ideal. This distortion results in erroneous data when restored to digital information by a receiver. Additionally, because the ability of systems to eliminate error is limited by the characteristics of their components, conventional systems having tolerated some degrees of deviation rather than solving the above fundamental problems.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a data transmission method and its apparatus in a PAM communication system that substantially obviates one or more of the limitations and disadvantages of the related art.
An object of the present invention is to provide a data transmission method and apparatus in a PAM communication system for preventing distortions from appearing in the PAM modulator output signals before they are transmitted to a channel. Depending upon the degree of the distortion, this and other objects and advantages can be accomplished by adjusting the binary data entering the PAM modulator to include information for compensating for the distortion generated by the operation of the actual PAM modulator, alone or in addition to improving the characteristics of the PAM modulator.
Additional features and advantages of the present invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure as illustrated in the written description and claims hereof, as well as the appended drawings.
To achieve these and other advantages, and in accordance with the purpose of the present invention as embodied and broadly described, a data transmission method in a PAM communication system which converts information to be transmitted into digital data, converts the digital signal to an analog signal, modulates the analog signal using a PAM modulator, and transmits the signal through a predetermined transmission channel, the method includes the steps of: measuring distortion of a signal to be transmitted to the transmission channel; generating compensation information corresponding to the distortion measured; and adjusting the digital data entering the PAM modulator based upon the compensation information generated. In the adjusting step described above, artificial distortion is generated at the digital data entering the PAM modulator based upon the compensation information generated at the generating step above.
The data transmission apparatus according to this invention includes a digital circuit for converting the input signal into the binary data; a D/A converter for converting the binary data input by the digital circuit into an analog signal; a filter for filtering the analog signal from the D/A converter according to a specified frequency limits; a matching unit for matching the signal output from the filter with the property of the transmission channel; a distortion compensation unit for altering the binary data according to predetermined compensation information before sending it to a PAM modulator, in order to minimize distortion when transmitting the signal through the transmission channel; a comparator for comparing distortion occurring when original binary data, input to a digital/analog (D/A) converter, is converted into PAM signal, filtered by a filter, and converted into a matching signal by a matching unit; and a compensation information generator for providing compensation information to the distortion compensation unit, allowing the distortion compensation unit to compensate for distortion of the original binary data according to the output of the comparator, before sending it to the D/A converter.
The distortion compensation unit contains a digital signal processor for adjusting the binary data generated by the digital circuit according to compensation information provided by the compensation information generator.
The compensation information generator contains ROM storing optimal compensation data so as to generate an address based upon the signal transmitted from the comparator, access data corresponding to the address, and generate compensation information.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
REFERENCES:
patent: 5854812 (1998-12-01), Huber et al.
Digital Communications Fundamentals and Applications, Prentice-Hall International Editions, Bernard Sklar, “
Kwon Ki-Jo
Yoon Young-Bin
Chin Stephen
Deppe Betsy L.
Hyundai Electronics Industries Co,. Ltd.
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