Communications: electrical – Continuously variable indicating – With meter reading
Reexamination Certificate
1999-10-25
2002-12-31
Pope, Daryl (Department: 2632)
Communications: electrical
Continuously variable indicating
With meter reading
C340S870030, C340S870030, C455S039000, C455S039000, C455S059000, C455S039000
Reexamination Certificate
active
06501388
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a radio signal selective-calling receiver, and more particularly to a radio signal selective-calling receiver which is capable of detecting a difference in frequency between a base clock signal of a base station and a base clock signal of the radio signal selective-calling receiver itself in paging system, and establishing synchronization.
2. Description of the Related Art
A signal processing system for a radio signal selective-calling receiver is grouped into NTT style and POCSAG (Post Office Code Standardization Advisory Group) style.
NTT style is a perfect synchronization system in which signals are always transmitted, whereas POCSAG style is a preamble synchronization system in which signals are transmitted only when necessary. In addition, NTT style puts emphasis on enhancement of a rate at which signals are intermittently received, whereas POCSAG style puts emphasis on shortening delayed time in calling.
A lot of radio signal selective-calling receivers have been suggested so far.
For instance, Japanese Patent Publication No. 64-3413 has suggested a radio signal selective-calling receiver which stores a plurality of calling numbers through a small-sized circuitry. The suggested radio signal selective-calling receiver includes a programmable read only memory (PROM) and a decoder equipped within PROM. The radio signal selective-calling receiver attempts to reduce the number of wirings connecting PROM to the decoder, by reading out in series what is stored in PROM.
Japanese Unexamined Patent Publication No. 2-218231 has suggested a radio signal selective-calling receiver which compensates for an oscillation frequency of a local oscillator with respect to temperature. The suggested radio signal selective-calling receiver includes a device having a capacity variable in accordance with an output of a stabilized power source, in a local oscillation circuit to thereby compensate for the local oscillation circuit with respect to temperature.
Japanese Unexamined Patent Publication No. 2-504096 has suggested a data communication device resulted from improvement of a pager. The suggested data communication device is designed to include a random access memory storing broadcast messages therein and amending operation of a selected pager through broadcasting, to thereby provide flexibility to pager's operation such as storage of data and retrieval of data.
Japanese Patent Publication No. 6-56976 has suggested a radio signal selective-calling receiver detecting signals in intermittent signal-receiving operation by counting the number of turning point signals inside and outside window signals which are in synchronization with synchronization clock signals.
The suggested radio signal selective-calling receiver is capable of stopping intermittent signal-receiving operation by subsequent signals, even though a specific pre-signal is not received, by detecting the counted number of turning point signals in the form of a signal.
A base clock signal of a base station in conventional paging system including the above-mentioned prior systems has an accuracy of ±100 ppm or smaller in accordance with the standard. However, some base stations in paging system now actually in use employs a base clock signal having an accuracy in the range of 400 to 500 ppm, which is remarkably out of the standard.
If a radio signal selective-calling receiver is situated in an area covered by a base station which transmits a base clock signal with less accuracy, a call is sometimes skipped in the radio signal selective-calling receiver when calls are received, because of a difference in bit.
Hereinbelow is explained how a preamble signal is recognized in POCSAG code.
A preamble signal illustrated in FIG.
1
(A) is a signal having been transmitted from a base station and demodulated by a radio signal selective-calling receiver in the case that there is no deviation in a base clock signal of a base station.
A signal illustrated in FIG.
1
(B) is a synchronization clock signal for introducing data into a radio signal selective-calling receiver, and is generated based on a base clock signal transmitted from a base station. A leading edge of the synchronization clock signal is overlapped turning points of the demodulated signals illustrated in FIG.
1
(A) to thereby establish synchronization in the unit of bit, and data is judged at a trailing edge of the synchronization clock signal.
Data is judged at the trailing edges of the synchronization clock signal illustrated in FIG.
1
(B), namely at T
1
, T
2
, T
3
, T
4
and T
5
. In the demodulated signal illustrated in FIG.
1
(A), assuming that a lower level is represented with zero (0) and a high level is represented with one (1), data has a value of zero at the time T
1
, for instance. Hence, the demodulated signal is recognized to have values 0, 1, 0, 1 and 0 at T
1
, T
2
, T
3
, T
4
and T
5
, respectively.
FIG.
1
(C) illustrates a preamble signal being demodulated, which signal is obtained when a base clock signal of a base station is negatively deviated in paging system. In the demodulated signal illustrated in FIG.
1
(C), assuming that a lower level is represented with zero (0) and a high level is represented with one (1), the demodulated signal has a value of zero at the time T
1
, for instance. Hence, if data is judged at the trailing edges of the base clock signal illustrated in FIG.
1
(B), data is recognized to have values 0, 1, 0, 1 and 1 at T
1
, T
2
, T
3
, T
4
and T
5
, respectively. Thus, the demodulated signal illustrated in FIG.
1
(C) is not properly recognized as a preamble signal.
Japanese Unexamined Patent Publication No. 10-150682 has suggested an apparatus for making communication between a base station and a mobile station and for compensating for a local oscillation frequency of the mobile station. The apparatus is comprised of a transmitter for transmitting a calling signal from the base station to the mobile station which calling signal is comprised of a frame synchronization signal and a data signal, a receiver for receiving the calling signal at the mobile station, and a compensator for compensating for a local oscillation frequency of the mobile station in accordance with a frequency of the frame synchronization signal having been received at the receiver.
Japanese Unexamined Patent Publication No. 10-145255 has suggested a radio signal selective-calling receiver including a capacitor having a capacity variable in accordance with a voltage applied thereto, a voltage source which applies a voltage across the capacitor, and a controller controlling a voltage generated by the voltage source.
Japanese Unexamined Patent Publication No. 10-56664 has suggested a radio signal calling receiver including first means for detecting deviation in synchronization by comparing synchronization signals transmitted from a base station, to each other while a synchronization detecting window is open, and for maintaining synchronization in accordance with the detected deviation, and second means for varying a period in which the synchronization detecting window is open, in accordance with a cycle at which radio signals are to be received which cycle is assigned to a pager.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a radio signal selective-calling receiver which is capable of detecting a difference in frequency between a base clock signal transmitted from a base station and a base clock signal of the radio signal selective-calling receiver itself, and accomplishing synchronization in the unit of bit.
It is also an object of the present invention to provide a method of receiving radio signals in a radio signal selective-calling receiver which method is capable of doing the same as mentioned above.
In one aspect of the present invention, there is provided a radio signal selective-calling receiver including (a) a detector which detects a difference in frequency between a first base clock signal of the radio signal selective-calling receiver
NEC Corporation
Pope Daryl
Young & Thompson
LandOfFree
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