Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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System For Converting a Paging Device To a Satellite Terminal
Field of the Invention
5 The present invention relates generally to paging communications systems and more particularly to wide
geographic area paging systems particularly directed toward a satellite based paging communications
system.
Background of the Invention
In the past, paging systems have provided service to a limited geographic area using a relatively high
power centralized ground tr~nsmitting site. This arrangement worked ~lpqu~t~ly in small cites and
municipalities, but often proved unsuitable for large metropolitan areas. To adequately serve a larger
geographic area, paging systems began to simulcast (i.e. transmit the same message at sllhstzl.lti~lly the
15 same time) from several ground transmitters strategically positioned to provide wide are coverage. In such
a system, an individual having a selective call receiver (pager) could receive information anywhere in the
metropolitan area.
Today, the trend in paging communication is to provide even greater geographic coverage. Nationwide
20 paging systems are often contemplated in an attempt to provide paging messages to customers without
regard to where they are in the United States (for example). One known multi-city paging system employs
satellites to transmit paging messages to ground repeaters in appr~xi~.lately eighty cities so that their
customers can be paged while traveling in any of the covered cities. Regrettably these more recent paging
systems still suffer from the limited geographical coverage that can be achieved by the ground repeaters.
Accordingly, a need exists for a paging communication system that provides everyone with convenient,
reliable and efficient paging service.
It is therefore an object of this invention to attempt to provide a device that will afford a more a
30 convenient paging service, provide paging service over extremely wide areas with essentially no coverage
gaps yet being compatible with existing service.
It is a further object of the invention, to provide a mobile base station for coupling with existing selective
call receivers, to convert these receivers, such as pagers and the like, into useful satellite terminals.
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It is an object of this invention to provide such a device that is capable of operating within FCC and
Industry Canada regulations for transmitters having low power signals, thus obviating a requirement for
licensing.
s
Summary of the Invention
Thus, in accordance with the invention, there is provided, a personal portable paging system cmllpliaillg: a
personal portable paging unit for receiving signals tr~ncmilted at a first predet~.rmined frequency; and, a
10 personal portable base station (located about the paging unit) for converting the paging unit into a satellite
terminal, said base station comprising receiving means for receiving a signal tr:~n.~mit1ed from a satellite
transmitter at a second predetermined frequency, and for re-transmitting the received signal to the paging
unit at the first predetermined frequency.
In accordance with the invention, there is further provided, a personal portable base station for use
with a personal portable paging device operable to receive signals at a first pre :letPrmined frequency. The
personal portable base station comprises receiving means for receiving a signal from a satellite station
tr~n.cmitted at a second predetermined frequency; conversion means for converting the received signal to
the first predetermined frequency; and, tr~nemitting means for tr~n~mitting the converted received signal to
20 the paging device at the first predetermined frequency.
In acc~,ldance with another aspect of the invention, a method is provided of coupling a portable pager with
a satellite system. The method Colllpl ises the steps of receiving a signal at a location about the portable
pager at a satellite tran.~mi1ting frequency; converting the signal to a first predetermined frequency
25 compatible with the operating frequency of the portable pager, and tr~n.~mitting the converted signal to the
pager at the first predetermined frequency.
In accordance with another aspect of the invention, a personal portable base station is provided, for use
with a personal portable paging device operable to receive signals of a first predetermined frequency. The
30 base station includes means for receiving a signal from a satellite station tr in~mitt~.d at a second
pre~lctl rmined frequency; conversion means for converting the received signal to the first predetermined
frequency; and, means for coupling the converted received signal to the personal portable paging device at
the first pre/1~ t~rmined frequency.
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Advantageously, the personal portable paging system in accordance with this invention, provides a
relatively inexpensive transceiver for converting a signal of one frequency to another, that allows a
commercially available pager to be utilized as a satellite terminal. The device can be designed to operate at
power levels that do not exceed governmental standards for small tr~ncmi1ting devices not requiring
5 licensing.
Brief Description of the Drawings
Exemplary embodiments of the invention will be described in conjunction with
10 the drawings, in which:
Fig. I is an illustration of a satellite system in accordance with this
invention.
Fig. Ib is an illustration of a satellite system similar to that shown in Fig. Ia including a circuit similar to
that of Fig. la, including a low power radio transmitter;
15 Fig. 2a is a circuit diagram of an embodiment of an MSAT paging terminal converter implementation
using a down converter and filter; and,
Fig. 2b is an alternative embodiment of an MSAT paging terminal converter implementation using a down
converter, filter, and up converter.
20 DetailedDes~ ,; on
Fundamentally, the present invention provides a continent-wide or global communication system designed
to call (page) individuals having a selective call receiver (pager). According to the invention, any
Cu~ )O~dly selective call receiver manufactured by any paging manufacturer may be used in the present
25 inventive system, that automatically adapts some portion of itself to accommodate the pager(s) that are
llP~ign ited to receive a paging message. As will become hereinafter apparent, the accommodating nature of
the present invention serves the individual (paging customer) using the pager, in that the operating range of
the paging device is greatly increased.
30 Throughout this specification, the term " about the paging unit" shall be hl~ d to mean within a range
and having a tr~n~mitting power and at frequencies not requiring licensing as a transmitting device. For
example, in North America, typically, the maximum allowable transmitting power would not exceed 12
nanowatts; however, this may vary slightly from one geographic region to another.
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At present, a satellite network exists for two-way communication of information. This network, commonly
referred to as Mobile Satellite Services ("MSS"), comprises a Communications Ground Segment ("CGS")
which consists of a Network Control Center and a Feeder-link Earth Station; a satellite; at least one mobile
transceiver; and the existing terrestrial data and telephone networks.
The system in accordance with this invention may operate as a single or dual mode system. The paging
devices to which it is designed can receive a same message simultaneously, or nearly simultaneously from
two different sources, thus, from both from a satellite and from terrestrial transmitters that broadcast over
10 the local area. Therefore, the mobile base station described hereafter and the local broadcaster transmit at
the same frequency. Alternatively in signal mode, the system can listen to either the satellite or the
terrestrial transmitter.
Referring now to Fig. Ia, a satellite system is shown, having a ground station 10, that transmits signals in
15 the Ku-band to a mobile satellite (MSAT) 12. The MSAT 12 retransmits the received Ku-band signals in
the L-band to mobile ground receivers 14. Each mobile receiver 14, in the form of a portable base station
is equipped with an antenna capable of receiving an L-band signals tr~ncmit~ed from the satellite 12 at a
frequency in the range of 1525 to 1559 MHz. The personal base station further includes circuitry for
converting the 1525 to 1559 MHz received L-band signal to a frequency in the range of 929 to 932 MHz
20 compatible with the native frequency of a conventional pager 16. After the signals are converted, they are
coupled to a pager 16 in one of two ways, shown in Figs. 2a and 2b respectively and later described. The
basic operation of the system shown in Fig. 1 is as follows: A message to be transmitted to a pager 16 is
sent by telephone through the public telephone network (PTN) to the ground station 10. The message is
sent as a Ku-band signal tr~n~mitted by the ground station 10 destined for the pager 16 within the purview
25 of the satellite 12. The signal is received by the satellite 12 and is retr:~ncmilt~.d in the L-band to the
personal base station. The base station 14 converts the L-band signal from a frequency of 1525 to 1559
MHz to a frequency of 929 to 932 MHz. Under most circumstances whether or not the pager is in the
vicinity of the ground station it will receive a message destined for it if coupled to the personal base station
14. Thus, in essence, the pager 16 coupled to the base station 14 becomes a mobile personal satellite
30 terminal. Since the personal base station receives, converts, and transmits signals, a plurality of pagers 16
proximate to a single base station can receive messages in this manner.
In the first embodiment shown in Fig. Ia, the circuitry 20 for converting the L-band signal to a 930 MHz
signal for coupling to the pager is shown. The circuit 20a includes an L-band antenna 24 coupled to a
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converter 22 for converting the received signal to a frequency of 930 MHz. The converter 22 is electrically
coupled to an adjacent terminal in the form of a paging device 16 for providing the paging device with a
compatible signal.
5 Turning now to Fig. lb, a second embodiment of the invention is shown. The circuit 20b is similar to that
of Fig. la, however, a low power radio transmitter (LPRT) 26 is electrically coupled to the converter 22.
The LPRT 26 is comprised of an amplifier 27 and a trAn~mitting antenna 28 that transmits a signal having a
maximum power of 12 nanowatts. Thus, one or more pagers 16 or like receiving devices must be
plo~ to the tran~mi~ting LPRT 26 in order to be electromagnetically coupled with it to receive the
10 tr~n~mi~ d signal. In a preferred embodiment, the LPRT 26 is designed to have a low enough power
obviating a requirement for a radio broadcast license.
One embodiment of the converter 22 is shown in Fig2a and includes amplifying means in the form of a low
noise amplifier (LNA) 221 for amplifying the received L-band signal and for providing the amplified
signal to a bandpass filter 222; the filter 222 ~ul~ lly filters out unwanted frequency components other
than those about 1.54 GHz; a mixer 224 receives the filtered 1.54 GHz signal and combines it with a
synthetically generated local oscillator frequency signal of 610 MHz. By combining/multiplying these two
signals together (1.54x 0.610), the 1.54 GHz signal is ~ul.~ lly converted to a 930 MHz signal. A
bandpass filter 226 is provided to filter out any unwanted frequencies substantially allowing only 930 MHz
20 frequency components to pass. The 930 MHz signal is amplified to the desired power level in an automatic
gain controlled or limiting amplifier 227 to ensure that the regulatory transmit power limits are not
exceeded The synthetically generated 610 MHz signal is conveniently provided, by a frequency synthesizer
225 slaved to a reference oscillator 228. The exact frequency of the synthesizer is typically programmed
via a micloc~ loller 229.
A second embodiment of the converter AAA is shown in Fig2b and includes amplifying means in the form
of a low noise amplifier (LNA) BBB for amplifying the received L-band signal and for providing the
amplified signal to a bandpass filter CCC; the filter CCC ~ub~l~llially filters out unwanted frequency
components other than those about 1.54 GHz; a mixer DDD receives the filtered 1.54 GHz signal and
30 combines it with a synthetically generated local oscillator frequency signal of 1454 MHz. By
combining/multiplying these two signals together (1.54x 1.454), the 1.54 GHz signal is substantially
converted to an 86 MHz signal. A bandpass filter EEE is provided to filter out any unwanted frequencies
substantially allowing only 86 MHz frequency components to pass. The 86 MHz signal is amplified to the
desired power level in an automatic gain controlled or limiting amplifier FFF to ensure that the regulatory
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transmit power limits are not exceeded. The 86 MHz signal is next presented to a mixer GGG and
combined/multiplied with a synthetically generated signal of 844 MHz. This results in the 86 MHz signal
being substantially converted to 930 MHz. A bandpass filter III is provided to filter out any unwanted
frequencies substantially allowing only 930 MHz components to pass. The synthetically generated signals
S at 1454 MHz and 844 MHz are conveniently provided, by frequency synthesizers JJJ and KKK slaved to
a reference oscillator LLL. The exact frequency of the synthesizers is typically programmed via a
microcontroller MMM.
Of course numerous other embodiments may be envisaged without departing from the spirit and scope of
the invention.
