 Portable radiotelephone and holder for mounting within a vehicle |
| Therefore, the present invention is made in view of the afore-mentioned disadvantages and an object ... |
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| Telephone dispenser with compact cord guide |
| Accordingly, it is an object of the present invention to provide a telephone handset that functions ... |
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| Power limiting circuit for radio communication device with a retractable antenna |
| The present invention relates to power control for a radio communication device having a ... |
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| User interface for a radio telephone |
| In accordance with the present invention there is provided a radiophone comprising a user interface ... |
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| Double-balanced mixer |
| What is claimed is: 1. A double-balanced mixer comprising: a diode ring with first symmetric inputs ... |
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| Method and apparatus for filtering engine exhaust |
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Paging method and apparatus
| Details |
Inventors: Wong, Gabriel K.; Tsui, Po S.;
Assignee: Digicomm, Ltd. (Hong Kong, HK)
Primary Examiner: Eisenzopf; Reinhard J.
Assistant Examiner: Le; Thanh
Attorney, Agent or Firm: Nixon & Vanderhye, P.C.
A two-way paging system utilizes four local frequencies for transmissions between pager units (22) and a central control station (20). A first local frequency (f.sub.1) carries a local clock; a second local frequency (f.sub.2) carries communications packets from the central control station to paging units; a third local frequency (f.sub.3) carries communication packets from the pager units to the central control station; and a fourth local frequency (f.sub.4) carries a status or request signal from the paging units (22) to the central control station (20). Transmissions on the fourth local frequency (f.sub.4) are in accordance with a time divided slot allocation among pager units accessing the central control station (20). For a two-way paging system having a plurality of central control stations (420.sub.x) servicing a corresponding plurality of cells, a total of eight frequencies are utilized within any one cell. Four of the utilized frequencies are the local frequencies (f.sub.1 -f.sub.4) ?which may differ from cell to cell!, and four of the utilized frequencies are lower power common frequencies or switching frequencies (C.sub.1 -C.sub.4) which are used to switch or hand-off a pager unit (422) traveling from one cell to another. |
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DETAILED DESCRIPTION OF THE DRAWINGS FIG.
1 shows a central control station 20 according to a first embodiment of the invention; FIG.
2 shows a paging unit 22 suitable for use with central control station 20.
As shown in FIG.
1, central control station 20 includes central computer 30; transmitter 32; receiver 34; and computerized telephone answering system 36.
Transmitter 32 transmits, via transmitting antenna 42, two local frequencies, namely frequency f.
sub.
1 and frequency f.
sub.
2.
Receiver 34 is connected to receiver antenna 44 for reception of two local frequencies, namely frequency f.
sub.
3 and frequency f.
sub.
4.
Computerized telephone answering system 36 is connected to a bank of telephones 48.
Central computer 30 of central control station 20 comprises a conventional computer equipped with typical components including a CPU 50; I/O interface 52; and memory 54.
Although shown only generally in FIG.
1, it should be understood that memory 54 includes a number of unillustrated memory devices, including (for example) a hard disk drive, RAM, and ROM.
FIG.
1 shows that memory 54 has stored therein (among other things) a pager registration file 55 and a pager directory file 56.
Pager files 55 and 56 are typically stored on a hard disk drive of central computer 30, and upon start-up are loadable into a RAM portion of memory 54.
Central computer 30 of central control station 20 further includes a decoder 57 (connected between receiver 34 and I/O interface 52 for decoding in-coming communications information from one or more pager units 22), as well as encoder 58 (connected between I/O interface 52 and transmitter 32 for encoding out-going communications information).
Central control station 20 also includes a clock unit 59 which generates a local clock signal f.
sub.
1 clk (which, in turn, is used to modulate frequency f.
sub.
1).
As illustrated further herein, CPU 50 of central control station 20 prepares communications packets for transmission on frequency f.
sub.
2.
As generally illustrated in FIG
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Ring Tones 
