Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1998-04-30
2001-05-08
Nguyen, Lee (Department: 2683)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S260000, C455S524000, C370S324000, C375S356000
Reexamination Certificate
active
06230021
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to wireless telecommunication technologies and, more particularly, to digital cordless communication systems including a plurality of stationary base stations for radio communication with multiple mobile communication units and main equipment for interconnection of such base stations to public telephone networks. The invention also relates to digital wireless communication systems with increased frequency stability of radio signals at plural base stations.
2. Description of the Related Art
One typical prior known digital cordless communication system of the type stated above has been disclosed, for example, in Published Unexamined Japanese Patent Application No. 6-318963 (“JP-A-6-318963”), wherein the system is designed to operatively associate with portable mobile communication units (also referred to as “handheld radiotelephone transceivers” or “personal stations” among those skilled in the art) having transmit-and-receive frequency stabilization functions.
FIG. 1
depicts a typical electronics configuration of one such personal station.
In
FIG. 1
the mobile personal station (PS) is generally designated by reference numeral
60
, which is constituted from a receiver circuit
602
which receives a digital radio frequency (RF) signal transmitted over-the-air from one base station—called the “cell station” in some cases—to an antenna
601
and then outputs an intermediate frequency signal, a frequency synthesizer
608
for supplying a local oscillation frequency signal to the receiver circuit
602
, a reference oscillator
607
for generation of a signal for use as a reference of frequency at the frequency synthesizer
608
, a demodulator
603
that is operable to reproduce or “play back” a carrier wave from the intermediate frequency signal as output from receiver
602
and also demodulate a received signal using as its phase reference signal a certain signal synchronized in phase with the carrier wave, a frequency counter
604
for counting up the frequency of such carrier wave reproduced by demodulator
603
, a frequency error detector section
605
that uses the count value of this frequency counter
604
to detect any possible frequency difference or “error” of the reference oscillator
607
, and a reference oscillator control circuit
606
responsive to receipt of an error detection signal from the frequency error detector
605
for controlling the oscillation frequency of reference oscillator
607
. It is thus possible, based on the frequency of a signal received from the cell station (CS), to achieve frequency stability of those signals as transmitted thereto from one or more mobile PSs.
Additionally, numeral
609
designates a modulator circuit for modulating a transmitted signal by the local oscillation signal fed from the frequency synthesizer
608
;
610
denotes a power amplifier for power amplification of the resultant transmit signal as modulated by the modulator
609
;
611
, a demodulation data monitor circuit of the demodulator
603
; and
612
, a reference signal control circuit of demodulator
603
.
Unfortunately, the prior art frequency stabilization scheme suffers from a problem in that upon failure of accurate synchronization of a reference clock signal in the frequency stabilization control loop employed in wireless CSs, any signal received from a CS is no longer used directly for frequency stabilization of mobile PSs because of the fact that the conventional system is inherently designed to effectuate intended PS frequency stabilization based on such received signal only.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a digital cordless communication system capable of avoiding the problem faced with by the prior art.
It is another object of the invention to provide an improved digital cordless telecommunication system capable of attaining and maintaining increased frequency stability of a reference clock signal for use as a reference in generating transmit signals in respective stationary base stations.
It is a further object of the invention to provide an improved digital cordless telecommunication system capable of attaining and holding superior frequency stability of a reference clock signal used as a reference in generating transmit signals in each base station, by use of either a high-precision “master” clock signal generated by main equipment or a master clock signal synchronized with such high-precision clock signal as received by a radio transceiver operatively associated with the main equipment.
A digital cordless communication system in accordance with a first principal aspect of this invention includes a plurality of stationary base stations located within respective geographical coverage regions assigned thereto for communication with multiple mobile communication units, and a system controller for connection of the base stations to a public telephone network. The system controller includes a high-precision oscillator which generates a master clock signal, whereas each base station includes a clock generator for receiving the master clock signal from the system controller for providing a reference clock signal as synchronized with the master clock signal.
A digital cordless communication system in accordance with a second aspect of the invention includes a plurality of base stations for over-the-air communication with personal communication units within respective geographical coverage areas or “zones” assigned to the base stations, a system controller for connection of the base stations to a public telephone network, and at least one radio receiver for outputting, upon receipt of a radio frequency (RF) signal as externally transmitted thereto, the received signal to the main equipment. The system controller includes a first clock generator for generation of a master clock signal synchronized with a signal being presently received at the radio receiver. Each of the base stations includes therein a second clock generator for receiving the master clock signal from the main equipment to generate a reference clock signal as synchronized to the master clock signal.
These and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.
REFERENCES:
patent: 5423058 (1995-06-01), Cudak et al.
patent: 5530704 (1996-06-01), Gibbons et al.
patent: 5612981 (1997-03-01), Huizer
patent: 5801783 (1998-09-01), Ross
patent: 6318963 (1994-11-01), None
Matsushita Electric - Industrial Co., Ltd.
Nguyen Lee
Stevens Davis Miller & Mosher LLP
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