Pulse or digital communications – Receivers
Reexamination Certificate
1995-12-29
2001-03-20
Tse, Young T. (Department: 2734)
Pulse or digital communications
Receivers
C375S271000, C455S042000, C455S044000, C455S205000
Reexamination Certificate
active
06205184
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to communication systems using narrow or very narrow band channels, so that the number of channels available for different types of communication systems (for example, cellular telephones, pagers, police/fire/rescue) can be increased. Specifically, the invention relates to a system and method for transmitting and receiving PM- or FM-based signals on narrow or very narrow band channels.
2. Related Art
In recent years, the VHF and UHF bands that were reserved to be allocated for use in communications have become highly congested, especially with the expanding use of cellular telephone and pager networks. However, due to restrictions imposed by current technology, government regulation and international agreement, the total available bandwidths in the VHF and UHF ranges, and consequently, the number of channels available in those band widths, are limited. With an expanding demand for communication systems which use those frequency bands, there is a growing need for a larger number of channels to be made available for allocation.
This need for more channels has led many manufacturers in the field to use higher frequency bands to avoid interference between channels and to achieve better frequency management. However, it is believed that using the higher UHF bands will expose users and operators to high frequency radiation that may cause health problems.
Another solution to the need for more channels which avoids the potential health risks involved in using the higher UHF bands is to increase the number of channels within the currently used frequency bands using a system with narrow channel bandwidths. However, such systems as currently designed produce poor sound quality and low data transmission rates.
Thus, there is a need in the art to provide transmission systems in which the information is transmitted in a narrow or very narrow bandwidth channel to provide a greater number of channels, but which still provides good sound quality at the receiving end.
SUMMARY OF THE INVENTION
The present invention is directed to providing a solution to the growing need for more channels, while overcoming the problems inherent in the current designs and implementations of narrow band systems.
The present invention provides a system for increasing the number of channels by using narrow band frequency modulation (FM) or Phase Modulation (PM), so that excellent sound quality levels and high data rates can be achieved. In particular, a purpose of the invention is to use narrow/very narrow band frequency or phase modulation transmitters and receivers to increase the number of channels, improve sound quality, increase the signal-to-noise ratio, increase the power of the transmitted information, and/or achieve high selectivity, high fidelity and/or low distortion.
In the present invention, a narrow band FM or PM signal transmission can be implemented by transmitting a signal in a narrow or very narrow frequency band, receiving the signal, converting the received signal to an IF (intermediate frequency) signal, and then expanding the narrow frequency deviation of the FM or PM signal. The narrow band frequency deviation is expanded by frequency-multiplying the IF signal. The frequency-multiplied signal may be converted to a low frequency signal or audio signal by a discriminator for further processing.
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“SL6601C Low Poer IF/AF PLL Circuit for Narrow Band FM, ”Linear Integrated Circuit Handbook, Plessey Semiconductors, Sep. 1985, pp. 121-123.
Jacobson Price Holman & Stern PLLC
Tse Young T.
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