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Mobile Phone Patent Abstract
A method and apparatus for detecting mobile phone in an Idle State
are disclosed. A signal-generating unit generates a pseudo base
station signal for transmission to a mobile phone in a detection
area. A detecting unit detects a response signal that the mobile
phone transmits in response to the pseudo base station signal. An
alarm-generating unit generates an alarm when the detecting unit
detects the response signal. Preferably, the pseudo base station
signal includes new zone information, such that the mobile phone
responds by transmitting a location registration signal which is
detected by the detecting unit. The method and apparatus are advantageous
in that they can apprise a mobile phone user within a specific area
that the user's mobile phone is turned on, by detecting the mobile
phone in Idle State passing a detection area. The method and apparatus
may prevent public injury or interference with electronic equipment
by restricting mobile phone use in a building or airplane.
Mobile Phone Patent Claims
What is claimed is:
1. An apparatus for detecting a mobile phone in an idle state comprising:
a signal-generating unit for generating a pseudo base station signal
based on zone information of neighboring base stations for transmission
to a mobile phone in a detection area; a detecting unit adapted
to detect a response signal that a mobile phone transmits in response
to the pseudo base station signal; and an alarm-generating unit
for generating an alarm when said detecting unit detects said response
signal.
2. The apparatus as set forth in claim 1, wherein said zone information
includes Pseudorandom Noise (PN) code offset, zone number, a system
identifier (SID) and a network identifier (NID).
3. The apparatus as set forth in claim 1, wherein said signal-generating
unit generates said pseudo base station signal using a system reference
clock derived from a Global Positioning System (GPS) receiver, said
GPS receiver receiving time-information from GPS satellites to generate
the system reference clock.
4. The apparatus as set forth in claim 1, further including circuitry
for analyzing neighboring base stations, said circuitry being adapted
to receive signals transmitted by neighboring base stations in an
overhead channel and extract neighboring base station information
therefrom, wherein said signal-generating unit generates said pseudo
base station signal based on said neighboring base station information.
5. The apparatus as set forth in claim 4, wherein said circuitry
for analyzing neighboring base stations comprises: (a) a first receiving
antenna for receiving radio frequency (RF) signals through the overhead
channel from neighboring base stations; (b) a first receiving filter
to filter said received RF signals; (c) a first frequency down-converter
to convert the filtered signal to a baseband signal; (d) a forward
demodulator to demodulate the baseband signal by despreading; and
(e) an overhead channel analyzer to analyze the demodulated signal
and generate said neighboring base station information.
6. The apparatus as set forth in claim 4, wherein said extracted
neighboring base station information includes transmit frequency
status, pilot signal strength and PN code offset.
7. The apparatus as set forth in claim 1, wherein said signal-generating
unit comprises: (a) a forward modulator for generating an overhead
channel signal using the reference clock received by said GPS receiver;
(b) an up-converter for converting the overhead channel signal to
an RF signal in a frequency band of a code division multiple access
(CDMA) system; (c) a transmit power amplifier for amplifying the
RF signal; (d) a transmitting filter for filtering the amplified
signal; and (e) a transmitting antenna for transmitting the filtered
signal as said pseudo base station signal.
8. The apparatus as set forth in claim 7, wherein said transmit
power amplifier amplifies the RF signal to a power level of only
several milliwatts, so as to prevent interference with electronic
equipment outside a specific detection area.
9. The apparatus as set forth in claim 7, wherein said transmitting
antenna transmits an overall forward frequency band of said CDMA
system, and forms a narrow beamwidth directed towards a specific
detection area.
10. The apparatus as set forth in claim 1, wherein said apparatus
transmits said pseudo base station signal in response to a signal
from an object detector indicating that an object is within a specific
detection area.
11. The apparatus as set forth in claim 1, wherein said detecting
unit comprises: (a) a second receiving antenna for receiving radio
frequency (RF) signals through an access channel from a mobile phone
in Idle State; (b) a receiving filter for filtering said received
RF signals; (c) a down-converter for converting the filtered signal
to a baseband signal; and (d) a reverse demodulator for despreading
and demodulating the baseband signal and forwarding an alarm signal
to an alarm-generating unit when said response signal of the mobile
phone is detected within said demodulated signal.
12. The apparatus as set forth in claim 11, wherein the frequency
separation, at a given time, between a passband of said receiving
filter and a transmitting filter of said signal generating unit
that filters said pseudo base station signal, is selected from the
group consisting of 45 MHz and 90 MHz.
13. The apparatus as set forth in claim 11, wherein said receiving
filter and a transmitting filter of said signal generating unit
that filters said pseudo base station signal each have a passband
of 1.25 MHz.
14. The apparatus as set forth in claim 1, wherein said signal-generating
unit comprises: (a) circuitry for generating said pseudo base station
signal at frequencies and a protocol of a code division multiple
access (CDMA) cellular system; and (b) circuitry for generating
said pseudo base station signal at frequencies and a protocol of
a CDMA personal communication service (PCS) system, and wherein
said detecting unit comprises: (a) circuitry for detecting a signal
that said mobile phone transmits at frequencies and a protocol of
a CDMA cellular system; and (b) circuitry for detecting a signal
that said mobile phone transmits at frequencies and a protocol of
a CDMA personal communication service (PCS) system.
15. The apparatus as set forth in claim 1, wherein said detection
area is an entranceway.
16. An apparatus for detecting a mobile phone in an idle state
comprising: (a) a GPS receiver for receiving time information from
a satellite and generating therefrom a system reference clock; (b)
a signal-generating unit for generating a pseudo base station signal
based on zone information of neighboring base stations for transmission
to said mobile phone in said idle state in a specific detection
area, said pseudo base station signal causing said mobile phone
in said idle state to transmit location registration signals; (c)
a detecting unit for detecting said location registration signals;
and (d) an alarm-generating unit for generating an alarm when said
detecting unit detects said location registration signals.
17. The apparatus as set forth in claim 16, wherein said signal-generating
unit generates said pseudo base station signal based on neighboring
base station information received through overhead channels transmitted
by said neighboring base stations.
18. The method of claim 17, wherein said pseudo base station signal
is transmitted in a standard overhead channel of a wireless communications
system.
19. A method for detecting a mobile phone in an idle state, said
method comprising the steps of: (a) transmitting a pseudo base station
signal within a detection area, using zone information of neighboring
base stations to generate said pseudo base station signal, and said
pseudo base station signal causing said mobile phone in said idle
state in said detection area to transmit a response signal; and
(b) receiving said response signal from said mobile phone and generating
an alarm.
20. The method of claim 19, wherein said pseudo base station signal
includes a pilot channel signal which is transmitted at a power
level sufficient for a mobile phone in said detection area to receive
said pilot channel signal with more power than pilot channel signals
of all neighboring base stations in the vicinity of said detection
area.
21. A method for detecting a mobile phone in an idle state, said
method comprising the steps of: (a) generating a pseudo base station
signal by a signal-generating unit using zone information of neighboring
base stations, said pseudo base station signal having new zone information;
(b) transmitting said pseudo base station signal to a mobile phone
within a detection area; (c) receiving said pseudo base station
signal and transmitting a location registration signal to a detecting
unit by a mobile phone in said idle state; (d) receiving the location
registration signal from the mobile phone by said detecting unit;
and (e) generating an alarm when said detecting unit receives the
location registration signal from said mobile phone.
22. The method as set forth in claim 21, wherein said step of generating
a pseudo base station signal comprises the steps of: (a) receiving
an overhead channel signal from a base station located near the
detection area; and (b) obtaining information of neighboring base
stations by analyzing the received overhead channel signals.
23. The method as set forth in claim 22, wherein the step of receiving
an overhead channel signal includes tuning to all possible overhead
channels used by base stations of a code division multiple access
(CDMA) system.
24. The method as set forth in claim 21, wherein the step of generating
a pseudo base station signal is performed when an object detection
signal is received from an object detector indicating that an object
has entered the detection area.
25. The method as set forth in claim 21, wherein said pseudo base
station signal is generated having time-related access parameters
of an access channel in which said mobile phone transmits said location
registration signal, said time-related access parameters being sufficient
to reduce transmission-time for the location registration signal
of said mobile phone.
26. The method as set forth in claim 21, wherein said pseudo base
station signal is generated sequentially in a plurality of overhead
frequency channels of a code division multiple access (CDMA) system.
27. The method as set forth in claim 21, wherein the step of receiving
the location registration signal is performed by sequentially tuning
to different frequency channels to enable reception of said location
registration signal in any one of said different frequency channels.
28. The method as set forth in claim 21, wherein the step of receiving
the location registration is performed by sequentially tuning only
to access frequency channels being used in base stations located
near the detection area, to enable reception of said location registration
Mobile Phone Patent Description
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for detecting
a mobile phone in an Idle State, and in particular, for generating
an alarm when the phone in Idle State enters an area where the usage
of the mobile phone is prohibited.
A typical cellular telephone system includes a plurality of base
stations, each of which services a geographical cell of a small-scale
area, thereby providing coverage over a wide area encompassed by
a multiplicity of such cells. The base stations are centrally controlled
by a mobile switching center (MSC) so that a mobile phone subscriber
can maintain communication when moving between cells.
Cellular phone systems are advantageous in that they provide service
to mobile phone subscribers within any cell covered by the system.
However, a drawback to the cellular system is that it may do harm
to the public order in an area where usage of the mobile phone is
prohibited. For example, if a mobile phone rings while receiving
a call in a concert or exhibition hall, the resulting noise is a
disturbance to the performance. Additionally, mobile phone signal
transmissions may interfere with the operation of sensitive electronic
equipment such as in a hospital or an airplane. Such electronic
equipment can be adversely affected by traffic channel signals as
well as control channel signals, such as those sent back and forth
between mobiles and base stations during the call set-up process,
or during the registration process when a mobile phone is first
turned on.
One conventional technique to restrict use of a mobile phone in
a specific area is to employ an apparatus for generating an interference
signal to essentially "jam" the mobile phone and thereby
prevent it from operating properly. FIG. 1 shows an embodiment illustrating
a prior art apparatus for generating an interference signal for
this purpose. An apparatus 11 generates an RF interference signal
so as to prevent use of a mobile phone inside a building 10. However,
in general, buildings have windows or other entrances for radio
waves from the exterior. As such, with the approach of FIG. 1, it
is impossible to completely shut out radio frequency entering from
external base stations attempting to communicate and/or send control
channel signals to mobile phones within the building. Another problem
is that the RF interference signal generated by apparatus 11 may
cause other electronic equipment to malfunction.
Another prior art technique for restricting mobile phone use involves
the deployment of magnetic material detectors in selected locations
to detect the presence of mobile phones, which have magnetic material
therein. FIG. 2 shows an embodiment of an apparatus for detecting
magnetic substances. When a body possessing an object 24 having
magnetic components enters through an entrance 21, a magnetic detector
22 established inside the entrance 21 detects the magnetic components
and transmits an alarm signal to an alarm generator 23, which then
sounds an alarm. A drawback to this approach is that it will detect
such phones and sound an alarm regardless of whether the phones
are in use.
Traditionally, in such restricted use environments, announcements
are made to the public exhorting mobile phone owners to shut off
power to their phones, but inevitably, some phones remain turned
on. Hence, there is a need for a system that automatically detects
use of a mobile phone in the Idle State in public areas.
SUMMARY OF THE INVENTION
The present invention is directed to a method and apparatus for
detecting the presence of a mobile phone in an Idle State, in which
the mobile phone is powered up but not performing communication.
Embodiments of the invention render it possible to detect, for example,
a mobile phone in the Idle State within a specific indoor area,
or upon entering an entranceway.
In an illustrative embodiment of the invention, there is provided
an apparatus for detecting a mobile phone in an Idle State, which
apparatus includes a signal-generating unit that generates a pseudo
base station signal for transmission to a mobile phone in a detection
area. A detecting unit detects a response signal that the mobile
phone transmits in response to the pseudo base station signal. An
alarm-generating unit generates an alarm when the detecting unit
detects the response signal. Preferably, the pseudo base station
signal is an overhead channel signal that includes new zone information,
such that the mobile phone responds by transmitting a location registration
signal which is detected by the detecting unit. The method and apparatus
are particularly advantageous in a code division multiple access
(CDMA) system.
The apparatus may further include a GPS receiver for receiving
time information from a satellite and generating a system reference
clock, and circuitry for receiving and analyzing neighboring base
station information transmitted by such base stations in overhead
channels. In this case, the signal generating unit generates the
pseudo base station signal using the system reference clock and
neighboring base station information. The pseudo base station signal
may be transmitted in a plurality of frequency channels of the communication
system to ensure successful reception by the mobile station. In
addition, the detection unit may sequentially tune to a plurality
of access channels to ensure reception of the location registration
signal.
Other objects and advantages of the invention will become apparent
upon reading the detailed description and upon reference to the
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The following detailed description, given by way of example and
not intended to limit the present invention solely thereto, will
best be appreciated when read in conjunction with the accompanying
drawings in which like reference numerals denote similar or identical
parts or features, wherein:
FIG. 1 illustrates a prior art system that generates an interference
signal to prevent use of a mobile terminal;
FIG. 2 depicts a prior art system for detecting magnetic objects;
FIG. 3 is a block diagram of an embodiment of an apparatus for
detecting mobile phones in accordance with the present invention;
FIG. 4 is a block diagram of an illustrative apparatus 200 for
analyzing neighboring base stations in accordance with the invention;
FIG. 5 depicts an embodiment of apparatus 300 for generating a
pseudo base station signal in accordance with the invention;
FIG. 6 is a block diagram of an embodiment of apparatus 400 for
detecting a signal sent by a mobile phone;
FIG. 7 illustrates forward and reverse frequency channels of a
code division multiple access (CDMA) system;
FIG. 8 illustrates forward and reverse frequency channels of personal
communication services (PCS) system;
FIG. 9 is a flow chart of an exemplary method for detecting a mobile
phone according to the present invention; and
FIG. 10 shows waveforms illustrating a location registration signal
of a mobile phone.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention provides a way to monitor whether a mobile
phone in a specific detection area is in an Idle State. An Idle
State is generally defined as a state in which the mobile phone
is powered-up in a standby mode, but is not engaged in active voice
communication. In the Idle State the mobile phone is waiting for
an incoming call that is detected through reception and analysis
of control channel signals transmitted by the base station. As soon
as control signals indicative of an incoming call are received by
the mobile phone, a call set-up process commences in which the mobile
terminal and base station begin exchanging messages. Thus, the present
invention, by detecting the Idle State condition, serves to prevent
subsequent transmission of radio signals by the mobile terminal.
On the other hand, if the mobile phone's power is off, it is not
registered with the local base station so the base station will
not transmit any signals to the mobile phone, and vice versa. Therefore,
the present invention is not designed to detect this condition.
Also, if the mobile phone is powered-on and communication is already
being performed, typically a supervisor in the restricted area or
building can detect such mobile phone use without any specific means,
so it is not considered in the present invention either. An apparatus
according to the present invention makes it possible to inform the
mobile phone user or the supervisor in the restricted area or the
like that the mobile phone is powered-on, by generating an alarm
when the mobile phone in the restricted area is detected in the
Idle State.
An illustrative embodiment of the present invention will be described
below in the context of a code division multiple access (CDMA) communication
system. However, it is to be understood that the present invention
is not so limited, and may be used in conjunction with other communication
protocols such as a time division multiple access (TDMA) system.
In a code division multiple access (CDMA) system, the reverse channel,
which is the communication link from the mobile phone to the base
station, includes an access channel and a traffic channel. The access
channel is a channel which enables the mobile phone to obtain information
to communicate with the base station. The traffic channel is used
to send and receive practical voice data to/from the base station
after communication is established through the access channel. The
present invention detects a mobile phone in the Idle State by using
the initial signal that the mobile phone transmits through the access
channel to a base station. This initial signal in the access channel
is typically a signal requesting registration with a new base station,
as will be explained further below.
The mobile phone in Idle State receives system parameters from
the wirelessly connected base station when the mobile phone's power
is initially on. The connected base station is assumed to be the
base station that primarily serves the cell in which the mobile
phone is located. (Base stations have overlapping coverage areas,
so it is possible for different base stations to service a mobile
phone at a given location.) The system parameters include frequency
to be tuned to by the mobile phone, pseudorandom noise (PN) code
offset to identify each base station, etc. The mobile phone, having
received the system parameters, maintains operation in the Idle
State, continuing to receive signals from the base station. The
mobile station in Idle State receives a pilot signal from the base
station, where the pilot signal contains the base station's own
PN code offset information.
At this time, if a second pilot signal using the same frequency
is received from a neighboring base station with higher signal strength
than the pilot signal of the present base station, where the second
pilot signal has different PN offset information, the mobile phone
tunes to the neighboring base station. The switchover of a mobile
phone in Idle State between base stations is called Idle handoff.
The mobile phone performing the Idle handoff does not send any signal
to the base station--it just receives parameters from the new base
station and stores them.
The mobile phone moving between base stations, if necessary, registers
its location to a mobile switching center through one of the base
stations such that only that one base station or its neighboring
base stations will be called when the mobile switching center calls
the mobile phone. That is, location registration is performed for
the purpose of facilitating call delivery to the mobile phone in
Idle State. Signals for location registration are transmitted to
the base station only by mobile phones in Idle State.
In accordance with the present invention, a detection apparatus
is provided which determines if a mobile phone is in the Idle State
by detecting whether a location registration signal is transmitted
from the mobile phone. The detection apparatus "tricks"
the mobile phone into transmitting a location registration signal
when the mobile phone passes through a detection area, by sending
a pseudo (or "dummy") base station signal to the mobile
phone.
The general process for performing location registration by a mobile
phone operating in a CDMA system is as follows. A parameter-based
location registration is performed when the system parameters received
from a new base station differ from the system parameters already
set up with the mobile phone. An order-based location registration
is performed when a location registration is ordered for a specific
mobile phone on the instructions of the base station. A timer-based
location registration is performed whenever a specific time passes
after performing the last location registration. In general, the
location registration is performed every two hours, so the probability
for the mobile phone to send the location registration signal within
a particular one-second time frame is 1/7200.
A zone-based location registration is performed when the mobile
phone enters a new zone. A cellular system divides the overall service
area into several zones and allocates a zone number characteristic
for each zone. The base stations located in a specific zone transmit
a common zone number associated with that zone through the paging
channel.
The embodiment described herein is implemented in a zone-based
location registration system to enable the mobile phone to be effectively
tricked into transmitting a location registration signal when it
enters a specific detection area. A detection apparatus according
to the present invention includes a signal generating unit that
transmits a pseudo base station signal including a new zone number
which has not been used in the cellular system. The mobile phone
in Idle State, when in the detection area, receives the signal and
recognizes that a new zone has been entered. The mobile phone responds
by transmitting a location registration signal through the access
channel for the purpose of registering in the new zone. The mobile
phone signal is detected by the detection apparatus, and an alarm
is sounded to indicate that the mobile phone has not been turned
off in the restricted area.
Each zone in a code division multiple access (CDMA) system is classified
according to the zone number, a system identifier (SID) to identify
the system providers, and a network identifier (NID) to identify
the networks of the mobile switching center. The mobile phone receives
values for these parameters from the base station and compares them
to values currently stored. If any of the new values is different
from the stored ones, it is determined that the mobile phone has
entered a new area, whereupon a location registration to a base
station in the new area is performed.
In light of the above, an illustrative detection apparatus according
to the present invention is equipped with circuitry for receiving
and analyzing information transmitted from neighboring base stations.
Such information includes each neighboring base station's zone number,
system identifier and network identifier, the transmit frequency
status, the pilot signal strength, the PN code offset, etc. The
detecting apparatus then selects area information different from
that of the neighboring base stations.
A preferred embodiment of the present invention will now be described
in detail with reference to the drawings.
FIG. 3 is a block diagram of an embodiment of an apparatus, 100,
for detecting a mobile phone in Idle State according to the present
invention. A GPS receiver 110 receives time information from satellites
and generates a system reference clock. An apparatus 200 for analyzing
neighboring base stations receives overhead channel signals from
neighboring base stations through antenna 210, and analyzes the
same to generate neighboring base station information. This information
is stored in memory 260. A signal-generating unit 300 generates
a pseudo base station signal based on the system reference clock
and the neighboring base station information. The pseudo base station
signal is transmitted to a mobile phone in the detection area via
antenna 350. A mobile phone MS in Idle State responds to the pseudo
base station signal by transmitting a location registration signal,
which is detected by a detecting unit 400 via antenna 410. An alarm-generating
unit 500 generates an alarm when detecting unit 400 detects a location
registration signal transmitted by the mobile phone in response
to the pseudo base station signal. A power supply 600 supplies operating
power to the various components of apparatus 100.
Antennas 350 and 410 are preferably situated in a location of the
restricted area such that isolated transmission and reception of
signals to and from a particular mobile phone in the restricted
area can be carried out. For instance, antennas 350 and 410 may
be located on the perimeter of an entranceway to achieve transmission/reception
of signals to/from mobile phones carried by persons passing through
the entranceway. To reduce the occurrences of unintentional communication
with mobile phones outside the restricted area, and the possibility
of interference with other electronic equipment, transmitting antenna
350 is preferably designed with a narrow beam that points to the
restricted area. Optionally, RF emissions are minimized to reduce
such interference by deploying an object detector 305 in the entranceway
or the like to detect the presence of a mobile phone or a person
in the first place, prior to any radiation by antenna 350. Whenever
an object is detected, object detector 305 sends a corresponding
signal to signal-generating unit 300, which responds by transmitting
the pseudo base station signal through antenna 350. Object detector
305 may operate, for example, by recognizing a change in weight
or light in the detection area.
Referring now to FIG. 4, a block diagram of an embodiment of the
apparatus 200 for analyzing neighboring base stations is shown.
Receiving antenna 210 receives RF signals through the overhead channel(s)
from neighboring base stations. A first receiving filter 220 excludes
out-of-band signals from the received RF signals. First frequency
down-converter 230 converts the filtered signal output by filter
220 to a baseband signal. A forward demodulator 240 demodulates
the baseband signal by means of a despreading operation. An overhead
channel analyzer 250 analyzes the overhead channel information of
the demodulated signal so as to extract the neighboring base station
information.
FIG. 5 is an exemplary embodiment of the signal-generating unit
300 which generates a pseudo base station signal in accordance with
the invention. The unit 300 includes a forward modulator 310 for
generating an overhead channel signal using the reference clock
received from GPS receiver 100 and the neighboring base station
information retrieved from memory 260. A frequency up-converter
320 converts the overhead channel signal to an RF signal at an appropriate
frequency used by the CDMA system. The up-converted pseudo base
station signal is amplified by transmit power amplifier 330, filtered
by transmitting filter 340 and radiated in the detection area by
antenna 350.
With reference now to FIG. 6, an embodiment of detecting unit 400
is illustrated in a block diagram. A second receiving antenna 410
receives RF signals in the access channel from a mobile phone in
Idle State. The received RF is filtered by second receiving filter
420 and down-converted to baseband by a second frequency down-converter
430. Reverse demodulator 440 despreads the baseband signal and activates
an alarm-generating unit 500 if the information contained within
the baseband signal corresponds to a location registration signal.
Processing circuitry for making this determination resides either
within the reverse demodulator 440 or within the alarm unit 500.
In order to detect signals from mobile phones and base stations
transmitted at all possible frequencies in the CDMA system, detection
apparatus 100 searches all usable frequencies in the CDMA system.
At present, there are two frequency bands commonly allocated for
CDMA wireless communications: the cellular system 800 MHz band and
the personal communication service (PCS) system 1800 MHz band. As
illustrated in FIG. 7, in the cellular system the reverse channel
from the mobile phone to the base station uses a 25 MHz band between
824 MHz and 849 MHz and the forward channel from the base station
to the mobile phone uses a 25 MHz band between 869 MHz and 894 MHz.
As illustrated in FIG. 8, in the PCS system the reverse channel
uses a 30 MHz band between 1750 MHz and 1780 MHz and the forward
channel uses a 30 MHz band between 1840 MHz and 1870 MHz. The frequency
separation between the forward and reverse channels is 45 MHz in
the cellular system and 90 MHz in the PCS system. In both the cellular
and PCS systems, CDMA frequency bands with 1.25 MHz wide bandwidths
may be used for each frequency channel. For example, if the transmit
frequency of the base station is F1, the transmit frequency of the
mobile phone to respond to the F1 signals should be (F1 plus 45)
MHz in the cellular system or (F1 plus 90) MHz in the PCS system.
Therefore, up-converter 320, down-converters 230, 430, transmitting
filter 340, and receiving filters 220, 420 operate in 1.25 MHz intervals
within a 55 MHz range (which is derived from 25 MHz plus 30 MHz).
For instance, receiving filters 220 and 420 are each bandpass filters
with an electronically controlled passband (1.25 MHz wide), the
center frequency of which is sequentially translated in steps of
1.25 MHz to sequentially capture the signals of adjacent channels.
The other components likewise operate in 1.25 MHz intervals to obtain
complete coverage over the whole CDMA band(s). Transmitting filter
340 and receiving filter 420 operate with 45 MHz (or 90 MHz) separation;
likewise, up-converter 320 and down-converter 430 operate with 45
MHz (or 90 MHz) separation.
Referring to FIG. 9 (to be read in conjunction with FIGS. 3-8),
a flowchart of an illustrative method for detecting a mobile phone
in the Idle State according to the present invention is presented.
The method begins in step s110, in which information is received
by antenna 210 in overhead channels from neighboring base stations
in the general vicinity of the detection apparatus. This information,
which is received and analyzed by apparatus 200 of FIG. 3, includes
zone information, PN codes, etc. of the neighboring base stations.
Apparatus 200 also analyzes the signal strengths of the respective
pilot signals and stores the signal strength information in memory
260. The signal strength information is used to ensure that the
ultimate pseudo base station signal to be transmitted will reach
the mobile phone in the detection area with more power than the
highest power pilot signal of the neighboring base stations.
The signal received at the receiving antenna 210 is transformed
into a baseband signal through the first receiving filter 220 and
the first frequency down-converter 230. The first receiving filter
220 searches the frequency bandwidth of 55 MHz by sequentially translating
its passband in 1.25 MHz intervals, thereby capturing signals from
all neighboring base stations. The baseband signal received on each
1.25 MHz frequency channel is despread by the forward demodulator
240. Overhead channel analyzer 250 decodes the despread signal to
analyze the status of all neighboring base stations such as the
strength of the pilot signal for each frequency channel, the zone
number, system identifier and network identifier, etc. The analysis
results for each frequency channel are stored in memory 260 and
used to generate the pseudo base station signal.
The overhead channel signal being received from a given neighboring
base station remains generally unchanged as long as the system configuration
stays the same. Therefore, it is unnecessary for overhead channel
analyzer 250 to operate at all times. Hence, to save operating power,
apparatus 200 can be designed to demodulate signals, analyze overhead
channels, etc., on a periodic basis rather than continually.
With continuing reference to FIG. 9, in step s120, signal generating
unit 300 utilizes the zone information of the neighboring base stations
stored in memory 260 to generate a pseudo base station signal that
contains new zone information. The pseudo base station signal is
an overhead channel signal generated by forward modulator 310, and
includes a system identifier (SID), network identifier (NID), new
zone number and new PN offset not used by any of the neighboring
base stations, etc. Tables 1 and 2 below represent a message format
that is typically used for transmission in the sync channel and
the paging channel (of the pseudo base station signal as well as
for neighboring base station signals). The forward modulator 310
generates the paging/sync channel signals for all paging frequency
channels being used by the neighboring base stations.
TABLE 1 Sync Channel Message Field Length (bits) Message type `00000001`
8 System identifier (SID) 15 Network identifier (NID) 16 PN code
offset (PILOT_PN) 9 System time (SYS_TIME) 36
TABLE 2 System Parameter message of Paging Channel Field Length
(bits) Message type `00000001` 8 PN code offset (PILOT_PN) 9 System
identifier (SID) 15 Network identifier (NID) 16 Registration zone
(REG_ZONE) 12 Zone timer (ZONE_TIMER) 3
The pseudo base station signal is transmitted to a mobile phone
in the detection area in step s130. Preferably, by employing object
detector 305 as discussed above in the detection area vicinity,
the pseudo base station signal is transmitted only upon the detection
of an object. In this manner, the total RF emissions are reduced
and electrical power is saved as well. If an object enters the detection
area, object detector 305 sends a specific signal to signal generating
unit 300, whereupon forward modulator 310 generates the pseudo base
station signal. The modulated signal is up-converted, amplified
and transmitted at an appropriate power level, e.g., a few milliwatts,
to the mobile phone via antenna 350. At this time, the pseudo base
station signal is generated and transmitted on all overhead channel
frequencies used by the neighboring base stations. Thus, the forward
modulator 310, up-converter 320, power amplifier 330, and filter
140 all operate at successive intervals of 1.25 MHz so as to generate
and transmit the pseudo base station signal at all possible overhead
channel frequencies in a short time interval. This ensures that
the mobile phone, which is typically tuned to only one of the 1.25
MHz channels, will properly receive the pseudo base station signal.
In step s140, the mobile phone receives the pseudo base station
signal and recognizes that it contains a new pilot signal with a
higher power level than the highest power pilot signal currently
being received. As a result, the mobile phone is tricked into beginning
the location registration process to register with the new (pseudo)
base station by tuning to the sync channel using the detected pilot
signal. The mobile phone obtains timing information of the pseudo
base station from the sync channel and searches the paging channel
using the timing information to extract the desired base station
information. It analyzes the area information included in the pseudo
base station signal, in particular, the zone number, system identifier
and network identifier, and compares those with the currently stored
area information (from the last neighboring base station that the
mobile phone registered with). Since the received area information
is different from the stored area information, the mobile phone
tunes to the pilot signal within the pseudo base station signal
and then transmits a location registration signal to detection apparatus
100 to demand a location registration.
FIG. 10 illustrates a location registration signal transmitted
by a mobile phone. To achieve location registration, the mobile
phone transmits an access probe sequence including a plurality of
probe signals repeatedly. Waveform (A) of FIG. 10 illustrates an
access probe sequence in which probe sequence signals are repeatedly
transmitted at time intervals T1. A maximum of 15 probe sequences
are transmitted. As illustrated by waveform (B), each probe sequence
contains up to sixteen access probes which are sequentially transmitted
at time intervals T2, with each successive probe signal having a
higher power level than the previous one by P1 power units. As illustrated
by diagram (C), each access probe signal includes preamble and message
portions each having a number of frames, e.g., 4 to 26 frames, each
20 ms in duration.
The mobile phone transmitting the above location registration signal
is provided with various access parameters such as T1, T2, the number
of frames in the access probe signal, the power level increment
P1, etc. These access parameters are transmitted from the base station
through the paging channel, and are determinative of the characteristics
of the location registration signal to be transmitted. If general
access parameters are used, it takes about one or two seconds for
the base station to recognize the location registration signal transmitted
from the mobile phone, assuming the location registration signal
frequency band is known by the base station.
Returning to FIG. 9, in step s150, detecting unit 400 searches
for and ultimately receives the location registration signal from
the mobile phone via antenna 410. That is, the received signal from
the antenna is applied to reverse demodulator 440 through the receiving
filter 420 and down-converter 430. Reverse demodulator 440 despreads
and demodulates the signal from down-converter 430 and then analyzes
the modulated signal to determine if a location registration signal
is present. When this signal is present, an alarm is generated by
the alarm unit in step s160 to alert the person carrying the mobile
phone or a supervisor that a mobile phone in Idle State is present
and should be turned off.
The signal searching operation of step s150 will now be considered
in more detail. Since the combined usable frequency band in the
reverse channels of the cellular system and PCS systems is 55 MHz
(i.e., 25 MHz plus 30 MHz, respectively), detection unit 400 may
be designed to perform a search for a location registration signal
within each 1.25 MHz frequency channel of the 55 MHz band. As a
result, assuming a 1.5 second search in each frequency band, it
would take about 66 seconds to search all the frequency channels
(where (55/1.25).times.1.5 seconds=66 seconds). The 66 second search
time thus represents the maximum time needed to detect a location
registration signal, assuming that the mobile phone may possibly
be transmitting in the last frequency channel searched. However,
66 seconds is too much time to be allocated for detecting a mobile
phone in most practical situations. One way to shorten the detection
time is for signal generating unit 300 to change the access parameters.
Table. 3 below represents a format of an access parameter message
transmitted by a base station through the paging channel.
TABLE 3 Access Parameter Message Format Field Length (bits) Message
type `00000010` 8 PILOT_PN 9 ACC_MSG_SEQ 6 ACC_CHAN 5 MAX_CAP_SZ
3 PAM_SZ 4 ACC_TMO 4 PROBE_BKOFF 4 BKOFF 4
To shorten the time required to detect the transmission of a location
registration signal by the mobile phone, the access parameters can
be changed. In this case, the signal-generating unit 300 transmits
the paging channel signal of the pseudo base station signal with
new access parameters. In particular, signal-generating unit 300
adjusts the time variables T1 and T2 to shorten the time required
to recognize the location registration signal of the mobile phone.
In general, CDMA service providers are allocated forward and reverse
channel bandwidths as wide as 10 MHz, to enable use of eight frequency
channels in total. Practically, however, the service providers use
only one or three frequency channels. Therefore, if only the one
or three frequency channels in current use are searched when signal-generating
unit 300 generates a pseudo base station signal and detecting unit
400 detects the location registration signal, the search time can
be shortened by 5/8 to 7/8 as compared to the case in which all
available frequency bands are searched.
Also, as the probability is high that the mobile phone in Idle
State is already tuned to one of the neighboring base stations,
detection apparatus 100 can be designed to operate, at any given
time, only at the frequency or frequencies being used in the neighboring
base station(s), rather than at all forward channel frequencies.
In this manner, the search time required by detecting unit 100 to
detect the location registration signal from the mobile phone can
be shortened dramatically, since the search need only be performed
at one or several frequency channels. Additionally, if detection
apparatuses for the cellular PCS systems are configured in parallel,
i.e., with one detection unit operating at the cellular band and
the other operating independently at the PCS band, the search time
can be further shortened.
From the foregoing, it should be readily appreciated that embodiments
of the present invention render it possible to call a person's attention
to the use of his/her mobile phone within a specific detection area
in advance by detecting if the mobile phone in Idle State passes
through the specific detection area. Consequently, it is possible
to prevent public injury and the possibility of causing electronic
equipment to erroneously operate by restricting mobile phone use
in a specific area. In addition, embodiments of the present invention
makes it possible to more precisely detect a mobile phone in Idle
State by recognizing a location registration signal of the mobile
phone as soon as possible.
While the invention is susceptible to various modification and
alternative forms, specific embodiments thereof have been shown
by way of example in the drawings and have been described hereinabove
in detail. It should be understood, however, that it is not intended
to limit the invention to the particular forms disclosed, but on
the contrary, the intention is to cover all modifications, equivalents,
and alternatives falling within the spirit and scope of the invention
as defined by the appended claims. |