Telecommunications – Transmitter and receiver at separate stations
Reexamination Certificate
1998-06-03
2001-08-07
Kincaid, Lester G. (Department: 2682)
Telecommunications
Transmitter and receiver at separate stations
C340S870030, C370S465000, C375S225000
Reexamination Certificate
active
06272318
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a pager of the POCSAG system, and in particular, to a pager capable of setting a plurality of transmission speeds through a change-over operation in an automatic fashion.
DESCRIPTION OF THE RELATED ART
Heretofore, in the pagers operating in the POCSAG system, the transmission speed (to be referred to as baud rate herebelow) is limited to either one of 512, 1200, and 2400 bits per second (bps; these baud rates will be referred to respectively as Abps, Bbps, and Cbps herebelow). Namely, the speed varies between service areas and network managing firms or network providers.
Therefore, one of the baud rates, i.e., Abps, Bbps, or Cbps is beforehand set in the pagers of the POCSAG system. In the following description, “baud rate (Abps, Bbps, Cbps)” indicates that either one thereof is to be used.
Specifically, the clock signal is set in association with the baud rate (Abps, Bbps, Cbps);
Moreover, the band of the low-pass filter (LPF) is accordingly changed or there is disposed a low-pass filter dedicated to the band.
In the pager of this type, an integrated circuit for demodulation and detection of signals in a radio section thereof includes a bit-rate low-pass filter to cope with each of the baud rates Abps, Bbps, and Cbps.
However, the decoder in the pager is adjusted to cope only with Abps, Bbps, or Cbps beforehand set as above.
Consequently, the conventional pager of the POCSAG system has been used only with one baud rate Abps, Bbps, or Cbps.
In the pager above, a broadcast radio wave received by an antenna such that the received signal is amplified by a radio section. The signal is subjected to a mixing operation and a frequency conversion. A band limiting operation is conducted for the obtained signal to limit a band thereof to resultantly attain a target intermediate frequency (IF) signal. The signal is demodulated by a demodulating section into a base band signal to be sent to a low-pass filter (LPF) to remove noise components therefrom. Additionally, the filter is adjusted to have a cutoff frequency corresponding to the baud rate Abps, Bbps, or Cbps of the POCSAG system to thereby accomplish the band limiting operation of the input signal. Furthermore, the base band signal is transformed by a comparator into a digital signal and is then collated with a selective call number (paging signal) beforehand stored therein. Notification of the results of the collation is carried out by operations of a central processing unit and a decoder.
FIG. 1
shows in a block diagram a configuration of a conventional decoder.
The decoder includes a reference signal generator
1
including a crystal oscillator Xtal to produce a clock signal. The clock signal and a digital base signal are fed to a bit synchronizing section
2
. The section
2
divides the input signal in accordance with the baud rate Abps, Bbps, or Cbps of the POCSAG system to generate a baud rate indication signal, i.e., a baud rate clock signal and then sends the signal to a signal processing section
3
. In accordance with the baud rate indication signal, the processing section
3
executes processing for the digital base band signal, i.e., the received signal. In short, the section conducts such operations as the collation between the paging number (signal) and a paging number beforehand stored in a read-only memory (ROM) and an operation to activate a notifying section.
As above, in the conventional pager, it is impossible to automatically select a baud rate for each of the service areas or the network providers. In other words, it is required to produce a pager set to each of the desired baud rates, which leads to a drawback of reduction in productivity of the pagers.
Furthermore, when the service area or the network provider in a service area is changed or when the baud rate is altered depending on the time zones, the baud rate of the pager is required to be readjusted, which results in deterioration in operability of the pager.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention, which has been devised to remove the problems of the prior art, to provide a pager capable of automatically selecting one of a plurality of different transmission speeds for each of the service areas or the network providers, which removes necessity of the production of pagers for the respective transmission speeds to thereby improve productivity of the pagers. Moreover, thanks to the pager, it becomes unnecessary to readjust the transmission speed even when the service area or the network provider in a service area is altered, which advantageously improves operability and usability of the pager.
To achieve the object above in accordance with a first aspect of the present invention, there is provided a pager for receiving a broadcast radio wave transmitted at one of a plurality of baud rates and automatically setting an operation mode thereof for a paging operation at the baud rate of the received signal. The pager is configured to include reception processing means for receiving the broadcast radio wave and producing a demodulated signal therefrom and automatic paging operation setting means for automatically setting an operation mode thereof for an operation at any one of a plurality of baud rates in accordance with the demodulated signal produced from the reception processing means and conducting a paging operation when a received paging number matches a selective paging number beforehand stored therein.
In accordance with a second aspect of the present invention, the automatic paging operation setting means conducts a voltage conversion for the received baud rates and automatically sets the operation mode, when a voltage resultant from the conversion is within a predetermined voltage range respectively corresponding to a plurality of predetermined baud rates, to an operation at the baud rate of the received signal.
In accordance with a third aspect of the present invention, the automatic paging operation setting means conducts, in association with the automatic setting of the operation mode to the operation at the baud rate of the received signal, a band limitation for the received signal of the reception processing means in accordance with the baud rate.
In accordance with a fourth aspect of the present invention, the reception processing means and automatic paging operation setting means include a radio section for amplifying a received signal obtained by receiving the broadcast radio wave and converting the signal into an intermediate frequency signal therefrom, a demodulating section for demodulating the intermediate frequency signal from the radio section, a low-pass filter for receiving as an input thereto a demodulated base band signal from the demodulating section and having a cutoff frequency set to a value corresponding to one of a plurality of baud rates in response to a switching signal, a comparator for converting the base band signal from the low-pass filter into a digital signal, a notifying section for notifying a signal reception, a decoder for receiving as an input thereto the digital base band signal from the comparator, correlating a received pre-stored paging number with a paging number activating the notifying section, and transmitting a switching signal to change the cutoff frequency of the low-pass filter, and a storage section for storing therein the paging number unique to the pager.
In accordance with a fifth aspect of the present invention, the decoder includes a reference signal generator for generating a clock signal as a reference of operation, a bit synchronizing section for outputting a baud rate indication signal corresponding to one of the plural of transmission baud rates, a phase comparing section for comparing a phase of the demodulated signal with a phase of the baud rate indication signal from the bit synchronizing section and transmitting an output voltage corresponding to the baud rate of the received signal, an analog-to-digital (A/D) converter for converting the output voltage from the phase comparing section into
Kincaid Lester G.
NEC Corporation
Ostrolenk Faber Gerb & Soffen, LLP
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