U.S. patent application number 10/157189 was filed with the patent office on 2002-12-05 for communication system and communication method with diversity features.
This patent application is currently assigned to MITSUBISHI MATERIALS CORPORATION. Invention is credited to Hosobuchi, Kenichiro, Nagira, Tumoru, Nakamura, Kenzo, Shibuno, Akira.
Application Number | 20020183083 10/157189 |
Document ID | / |
Family ID | 18095766 |
Filed Date | 2002-12-05 |
United States Patent
Application |
20020183083 |
Kind Code |
A1 |
Nagira, Tumoru ; et
al. |
December 5, 2002 |
Communication system and communication method with diversity
features
Abstract
A communication system and a communication method arranged to
obtain a diversity effect in mobile communication, to reduce the
influence of multipath interference, fading or the like, to perform
comparatively simple information communication such as message
communication with improved reliability, and to achieve effective
utilization of frequencies. A plurality of base stations having
receivers are provided around an urban area within base station
zones. The base stations repeatedly transmit the same message data.
Receiving repeaters are provided in the urban area and small or
medium suburban zones. Each receiving repeater relays a signal from
a small mobile terminal via an Internet network if the output level
of the mobile terminal is so low that direct transmission to one of
the base stations is impossible. A 25 kHz frequency band is divided
into four narrower bands of 6.25 kHz in one of the embodiments. Of
frequencies f1, f2, f3, and f4 in these bands, frequencies f1 to f3
are used for "down data transmission" from the base stations to a
mobile terminal while f4 is used for "up data transmission" from
the mobile station to one or more of the base stations.
Inventors: |
Nagira, Tumoru; (Omiya-Shi,
JP) ; Nakamura, Kenzo; (Omiya-Shi, JP) ;
Hosobuchi, Kenichiro; (Omiya-Shi, JP) ; Shibuno,
Akira; (Omiya-Shi, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
MITSUBISHI MATERIALS
CORPORATION
Tokyo
JP
|
Family ID: |
18095766 |
Appl. No.: |
10/157189 |
Filed: |
May 30, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10157189 |
May 30, 2002 |
|
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|
09192532 |
Nov 17, 1998 |
|
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6400959 |
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Current U.S.
Class: |
455/503 |
Current CPC
Class: |
H04W 88/04 20130101;
H04W 92/02 20130101; H04W 16/26 20130101; H04B 7/2606 20130101 |
Class at
Publication: |
455/503 ;
455/63 |
International
Class: |
H04B 001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 19, 1997 |
JP |
9-318123 |
Claims
What is claimed is:
1. A communication system having a first area where communication
with a mobile terminal can be performed and a second area where
communication can be performed with the mobile terminal when on a
periphery of the first area, said system comprising: a plurality of
base stations provided on the periphery of the first area, each of
said base stations being configured to communicate via wireless
communication in the first area, down message data being
transmitted on a first frequency in a first narrow band of a
channel frequency from an originating base station of said
plurality of base stations, each of the other plurality of base
stations configured to receive the down message data and then
transmit the down message data on the first frequency; and a mobile
terminal configured to receive the down message data transmitted
from the originating base station and other base stations and
configured to transmit up message data to the plurality of base
stations by using a second frequency in a second narrow band of the
channel frequency different from the first frequency used for
transmission of the down message data.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a communication system and
a communication method which enable communication with a mobile
terminal and, more particularly, to a communication system and a
communication method which enable comparatively simple information
communication, such as short-message communication, using a mobile
communication system to be performed with improved reliability in
an environment in which the influence of multipath interference,
fading or the like upon communication is considerable. The present
invention also relates to a communication system and communication
method which enable effective use of frequencies for the
above-mentioned kind of communications or the like.
[0003] 2. Description of the Related Art
[0004] Various communication systems have been proposed for
information communication with a mobile terminal. For example,
communication systems described below may relate to the present
invention.
[0005] A specialized mobile radio (SMR) communication system is a
system enabling communication in a large-zone service area by
placing a base station at the center of one area (zone)
corresponding to the service area. This communication system,
however, requires frequencies in a wide band for communication with
many users in the large zone.
[0006] A cellular communication system has a service area zone
divided into a group of a large number of small zones (cells), and
has base stations respectively placed in the small zones to perform
transmitting and receiving by using different frequencies
respectively assigned to the zones. That is, to enable
communication in a large-zone service area, a multiplicity of base
stations is provided to cover the entire service area. In the
cellular system, different frequency bands are used in cells
comparatively close to each other, and frequencies in the same band
can be used for cells which are located at such distances from each
other that jamming therebetween can be ignored. Therefore, the
overall frequency band for the cellular system can be smaller than
that for the SMR system. However, since the frequency bands for
cells which are located so close to each other that jamming can
occur, as well as the frequency bands for adjacent cells, are set
different from each other, the overall frequency band necessary for
the cellular system is substantially wide, though not so wide as
that for the SMR system.
[0007] Various mobile information communication systems presently
used, including the SMR and cellular communication systems, require
a disadvantageously wide frequency band, as described above.
Available frequency bands are restricted, and there is a limit to
use of frequencies in a wide band.
[0008] For example, with respect to communication using a simple
message, use of frequencies by the SMR communication system or
cellular communication system is uneconomical. In particular, the
conventional communication systems are being used mainly for speech
communication or telephone communication and subordinately for
message data and other kinds of data.
[0009] In mobile communication, particularly in communication in an
urban area, a problem of interference such as multipath
cancellation and fading due to the existence of buildings is
encountered. To cope with multipath cancellation or fading, trials
have been made with a diversity system or the like. If such a
system is used, a problem of a considerable increase in facility
price arises. In particular, when communication with a mobile
terminal is performed, the condition of interference such as
multipath cancellation and fading changes continuously, and it is
difficult to cope with such interference.
[0010] As determined by the present inventors there is a demand for
an apparatus (facilities) of a lower price for communication using
a particularly simple message data. However, including ways for
coping with multipath cancellation and fading will likely increase
the facility price. If the apparatus is made without such features
due to price controls, the rate of bit error in received data is
increased, resulting in a considerable reduction in communication
accuracy or, in some case, occurrence of communication failure.
[0011] In a multichannel communication system, such as a cellular
communication system, using a small-power output, outputs of a
multichannel transmitter may be output by being collectively
amplified by one wideband amplifier. In other general cases,
however, a combiner for combining outputs is used and a duplexer
filter or a similar circuit for separating a transmission frequency
and reception frequency from each other is also used for the
purpose of eliminating mutual interference between channels.
However, if such signal processing is performed, a signal loss is
caused and the antenna output is considerably reduced. If the power
is increased to avoid such an undesirable effect, a need to
increase the withstand voltage of electronic circuit components and
to provide other various processing techniques arises, resulting in
an increase in circuit complexity and an increase in the price of
the apparatus.
[0012] On the other hand, trails have been made using Internet
communication systems. Internet communication systems have been
used by being annexed to systems using mobile terminals because of
matching in terms of system configuration or because of the
relationship with the telephone number system. Considering the
efficiency of connection of communication systems, the present
connection to Internet communication systems cannot be regarded as
suitable.
SUMMARY OF THE INVENTION
[0013] An object of the present invention is to address the
above-described and other problems and provide a communication
system and a communication method which are simple in system
configuration, but which enable reliable message communication.
[0014] Another object of the present invention is to provide a
communication system and a communication method which enable
uniform communication with a reduced bit error anywhere in urban
zones crowded with buildings, suburban zones where buildings are
scattered, and so on.
[0015] Still another object of the present invention is to provide
a communication system in which an Internet system is incorporated
as a "wired" circuit, which can be formed of comparatively
low-priced system components, i.e., existing communication and date
processing systems and communication apparatus, and which can be
easily operated.
[0016] A further object of the present invention is to provide a
communication system and a communication method arranged to make
effective use of frequency bands and to enable communication in a
restricted frequency band.
[0017] To achieve these and other objects, according to one aspect
of the present invention, there is provided a communication system
having a first area where communication with a mobile terminal can
be performed and a second area where communication with a mobile
terminal on the periphery of the first area can be performed. This
communication system has a plurality of base stations provided on
the periphery of the first area, each of the base stations being
capable of communication in the first area, the base stations being
capable of communicating with each other in a wireless
communication manner. Downlink (down) message data is transmitted
on a frequency in a first narrow band from one of the base
stations. Each of the other base stations receiving the message
data sends out the message on the same frequency as the frequency
on which the message data has been received. A mobile terminal
which receives a signal transmitted from the originating and other
base stations transmits uplink (up) message data to the base
stations by using a frequency in a second narrow band different
from the frequency for transmission of the down message data.
[0018] Transmission of down message data from the base station is
performed in the first narrow band of, for example, 6.25 kHz. Each
of the other base stations receives this down message data and
sends out the received message data on the same frequency as that
on which it has received the message data. In this manner, the same
message data is sent out from the plurality of base stations,
thereby enabling a mobile terminal to receive a receivable one of
the transmitted data groups. Thus, a diversity effect is achieved
due to the redundancy in transmission. As a result, the influence
of multipath interference or fading can be reduced. The mobile
terminal receiving the message data sends up message data to the
base stations on a frequency in a band different from the first
narrow band. As described above, frequencies in different bands are
used for transmission of down message data and transmission of up
message data. For this communication system, no complicated
communication protocols are used.
[0019] Preferably, at least one of the plurality of base stations
is wire-connected to a wire communication network, and a receiving
and repeating mechanism is provided which is wire-connected to the
wire communication network, and which receives, in the
communication possible area, a signal transmitted from a mobile
terminal, and relays the signal via the wire communication network
to the base station connected to the wire communication network.
When the receiving and repeating means receives data transmitted
from the mobile terminal, it sends the received data to the base
station via the wire communication network in a wire communication
manner.
[0020] The receiving and repeating mechanism receives message data
transmitted from a mobile terminal when the output level of the
mobile terminal is low, when the communication condition is not
good, or when up message data cannot be directly transmitted to any
of the base stations. The receiving and repeating means sends the
data in a wire communication manner via the wire communication
network, e.g., an Internet network to the base station connected to
the Internet network. As a result, communication can be performed
without being affected by multipath interference or fading
regardless of the location of the mobile terminal.
[0021] More preferably, the originating base station that received
the above-mentioned down message monitors the state of transmission
of the message between the base stations and transmits a next
message data on a frequency in a third narrow band different from
the frequencies in the first and second narrow bands. Each of the
other base stations receiving the next message data sends out the
received message data on the same frequency as the frequency on
which the message data has been resolved. A mobile terminal
receiving a signal transmitted from the originating and other base
stations transmits up message data to the base stations by using a
frequency in the second narrow band different from the frequencies
for transmission of the above-mentioned down messages.
[0022] The next down message data transmission is performed by
using a frequency different from the frequency for the preceding
down message transmission. Thus, message data transmission is
performed at different times by using different frequencies, so
that no jamming occurs. Although two narrow frequency bands are
used, the width of each frequency band is narrow and the overall
band width is limited.
[0023] More preferably, a subscriber's terminal is wire-connected
to the wire communication network, and message data from the
subscriber's terminal is transmitted as a down message via the wire
communication network from the base station connected to the wire
communication network.
[0024] In this manner, message data can be transmitted from a
subscriber's terminal.
[0025] Specifically, the above-mentioned narrow frequency bands
have a width of 6.25 kHz.
[0026] Also, specifically, the above-described wire communication
network includes an Internet communication network.
[0027] According to another aspect of the present invention, there
is provided a communication method using a first area where
communication with a mobile terminal can be performed, a second
area where communication with a mobile terminal on the periphery of
the first area can be performed, and a plurality of base stations
provided on the periphery of the first area, each of the base
stations being capable of communication in the worst area, the base
stations being capable of communicating with each other in a
wireless communication manner. This communication method includes
the steps of transmitting down message data on a frequency in a
first narrow band from one of the base stations, sending out, from
each of the other base stations receiving the message data, the
received message data on the same frequency as the frequency on
which the message data has been received, and transmitting, from a
mobile terminal receiving a signal transmitted from the originating
and other base stations, up message data to the base stations by
using a frequency in a second narrow band different from the
frequency for the transmission of the down message.
[0028] Preferably, at least one of the plurality of base stations
is wire-connected to a wire communication network. When
communication is performed by providing a receiving and repeating
mechanism wire-connected to the wire communication network and
capable of receiving in the communication possible area a signal
transmitted from a mobile terminal and relaying the signal via the
wire communication network to the base station connected to the
wire communication network, the receiving and repeating mechanism
receiving data transmitted from the mobile terminal sends the
received data to the base station via the wire communication
network in a wire communication manner.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] A more complete appreciation of the invention and many of
the attendant advantages thereof will be readily obtained as the
same becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
[0030] FIG. 1 is a block diagram or a communication system in
accordance with the present invention;
[0031] FIG. 2 is a diagram showing the connections between
transmitters, receivers and so on in the system shown in FIG.
1:
[0032] FIG. 3 is a diagram showing the configuration of base
stations BA to BC, a receiving repeater RR and a mobile
terminal;
[0033] FIG. 4 is a diagram showing the configuration of a center
unit;
[0034] FIG. 5 is a diagram showing a method of using channel
frequencies:
[0035] FIG. 6 is a diagram showing the relationship between base
stations and channel setting with frequency bands f1 to f3 used for
communication between the base stations; and
[0036] FIG. 7 is a diagram showing the relationship between mobile
terminals and channel, frequencies.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0037] Referring now to the drawings, where common elements are
commonly labeled in the several views, FIG. 1 is a schematic
diagram of the configuration of a communication system in
accordance with the present invention, and FIG. 2 is a diagram
showing connections between base stations, receivers and so on
shown in FIG. 1.
[0038] Referring to FIG. 1, a central circular region indicated by
a thick line is an urban area, and each of circular regions
indicated by broken lines and containing the region representing
the urban area is called a base station region (base station zone).
In this embodiment, three base station zones 2A to 2C are provided
and base stations BA to BC are installed in these base station
zones 2A to 2C and around the urban area. The base stations BA to
BC respectively have receivers RA to RC. The base stations BA to BC
have their respective areas to cover in the urban area and are
capable of wireless communication in the circular areas (zones)
indicated by the broken lines.
[0039] The urban area is, for example, a region where there are a
number of multistory buildings such that the possibility of
occurrence of communication failure such as multipath cancellation
or fading is high.
[0040] The area extending outside the boundary of the urban area
represented by the thick-line circle is a suburban area. One base
station zone, e.g., the base station zone 2A overlaps both the
urban and suburban areas.
[0041] A mobile terminal can move between arbitrary points in the
urban and suburban areas, and is capable of communication in its
communication area.
[0042] Small or medium communication zones are prescribed in the
urban and suburban areas. Receiving repeaters RR are placed in the
small or medium zones. Each of the receiving repeaters RR performs
a relay operation of a signal from a small mobile terminal to one
of the base stations if the output level of the mobile terminal is
not high enough for direct transmission to the base station. That
is, since the output level of a small mobile terminal is low, the
receiving repeater receives data transmitted from the small mobile
terminal and retransmits the data to the base station through a
wire circuit in an Internet network 20, thus enabling transmission
from the mobile terminal to a desired transmission destination via
the base station. If a mobile terminal has a sufficiently high
output level, the mobile terminal can transmit directly to the
nearby base station without relaying by the receiving repeater
RR.
[0043] The configuration of the communication system shown in FIG.
1 and connections between the components of the communication
system will be described with reference to FIG. 2.
[0044] As mentioned above, the base stations BA, BB, and BC
respectively have receivers RA, RB, and RC. Each of the receivers
RA, RB, and RC has a receiving antenna. Each of the base stations
BA, BB, and BC has a transmitting antenna.
[0045] A center unit CENT is provided in the vicinity of the base
station BA and is connected, by an Internet provider, to the
Internet network 20 formed as a wire communication network via a
wire circuit, e.g., a dedicated line, a public system telephone
network (PSTN), an integrated services digital network (ISDN) or
the like, a PSTN in this embodiment. In FIG. 2, asterisk symbols
designate an Internet provider.
[0046] In the connections in the communication system illustrated
in FIG. 2, the Internet network 20 is wire-connected via the PSTN
to the central station CENT connected to the base station BA. The
Internet network 20 is also connected to each of the receiving
repeaters RR via an Internet provider. Each receiving repeater RR
is also connected to the Internet network 20. Accordingly, the
receiving repeater RR and the base station BA can be wire-connected
to each other via the Internet network 20.
[0047] It is not necessary that all the base stations be connected
to the Internet network 20. However, at least one of the base
stations is wire-connected to the Internet network 20. In this
embodiment, the base station BA is wire-connected to the Internet
network 20.
[0048] All the receiving repeaters are connected to the Internet
network 20. This is because each receiving repeater RR receives
data by wireless communication and transmits received data to other
communication apparatuses via the Internet network 20 while the
base stations capable of mutual wireless communication can
communicate with each other by transmitting data received from the
Internet network 20 if one of the base stations is connected to the
Internet network 20.
[0049] FIG. 3 is a diagram showing the configuration of the base
stations BA to BC, the receiving repeaters RR and a mobile
terminal.
[0050] Each of the base station shown in FIG. 3 has a transmitting
unit TX having an antenna 1, a transmitting circuit 2 and a
modulator 3, and a receiving unit R having a receiving antenna 6
and a receiver 7. The transmitting circuit 2 selectively uses a
plurality of channel frequencies, as described below, and therefore
includes a circuit for selecting one of the channel
frequencies.
[0051] Connected to the base station BA is the center unit CENT
having a data processor and memory section 4 and a line interface
(I/F) 5. In more detail, referring to FIG. 4, the center unit CENT
is also connected to the Internet network 20 via the wire circuit
22 and an Internet provider 27 (27A and 27B in FIG. 4).
[0052] Thus, no special circuits are required to form each of the
base stations BA to BC, and existing circuits can be used for the
base stations. As a result, the base stations can be simple in
configuration.
[0053] In this embodiment, the Internet network 20 is used because
it enables simplification of the system configuration because no
switchboards (or switch circuits) are used. Any network other than
the Internet network 20 may alternatively be used if it is
effective in simplifying the system.
[0054] A mobile terminal P which can send out a message has an
antenna 8, a transmission shared section 9, a data processing and
display operation section 10, a receiver 11, and a battery 19 for
supplying power to these circuits.
[0055] Each receiving repeater RR has an antenna 12, a receiver
section 13, a data processor and memory section 14, and a line
interface (I/F) 15. Each receiving repeater RR is connected to a
wire circuit 23 and to an Internet provider 28 via the line
interface 15 to be connected to the Internet network 20. Thus, the
receiving repeater is also simple in configuration.
[0056] A subscriber's terminal 227 is also connected to the
Internet network 20 via a wire circuit 21 and an Internet provider
26. This connection enables data to be transmitted from the
subscriber's terminal 227 to the base station BA via Internet
network 20, thereby enabling wireless communication to the other
base stations and transmission to mobile terminals.
[0057] FIG. 4 is a diagram of the configuration of the center unit
CENT shown in FIG. 3.
[0058] As mentioned above, the center unit CENT has the data
processor and memory section 4 and the line interface (I/F) 5.
[0059] The line interface 5 receives, via the Internet network 20,
wire circuits 22A and 22B and Internet providers 27A and 27B,
message data from the subscriber's terminal 227 and data from the
receiving repeater, i.e., message data from the mobile terminal
received by the receiving repeater. These received data groups are
output to the data processor and memory section 4.
[0060] The data processor and memory section 4 has a first data
processor 41 and as second data processor 42.
[0061] The data processor and memory section 4 has memories placed
between the first data processor 41 and the second data processor
42, i.e., a first memory 431 for storing "down message data
sequence" from the subscriber's terminal 227, second memory for
storing incoming confirmation data from the subscriber's terminal
227, and a third memory 433 for storing sending confirmation data
sent from the mobile terminal P to the subscriber's terminal 227.
Each of these memories 431 to 433 is a first-in/first-out (FIFO)
type memory such that data input earlier from the first data
processor 41 is first output to the second data processor 42. That
is, data from the first data processor 41 is temporarily stored as
a data sequence in each of these memories before it is output to
the second data processor 42.
[0062] The first to third memories are shown to be separate from
each other as illustrated in FIG. 4. These memories, however, may
be combined into one memory unit or may be formed separately and
independently as illustrated in FIG. 4.
[0063] The first data processor 41 also processes data received
from the receiver 7 by the same signal processing as that described
above, as well as data received from the line interface 5.
[0064] The second data processor 42 processes data from the memory
43, and supplies the processed data to the modulator 3. The data is
sent out as "down message" via the transmitting circuit 2 and the
antenna 1.
[0065] The basic operation of the transmitter TX, the center unit
CENT and the receiving repeater RR will be described with reference
to FIGS. 1 to 4.
[0066] The first data processor 41 at an upstream point of a
message data flow is connected to the line interface 5. The line
interface 5 receives a message from the mobile terminal and a
message from the subscriber's terminal 27. The line interface 5
receives these messages respectively from the first Internet
provider 27A connected to the Internet network 20 via the wire
circuit 22A and from the second Internet provider 27B connected to
Internet network 20 via the wire circuit 22B.
[0067] The first data processor 41 processes the message from the
terminal and the message from the subscriber's terminal 227
received by the line interface 5 and outputs the processed data to
the first to third memories 431 to 433 by referring to the contents
of the messages.
[0068] The first data processor 41 also receives received data
which has been received by the receiving antenna 6 and supplied
from the receiver 7, processes the data received by the receiving
antenna 6 in the same manner as it processes received data from the
Internet network 20, and outputs the processed data to the
corresponding one of the first to third memories 431 to 433.
[0069] The second data processor 42 processes data sequences output
from the first to third memories 431 to 433, and outputs the
processed data to the modulator 3 in the transmitter TX. A signal
formed by modulation with the data in the modulator 3 is
transmitted in the zone shown in FIG. 1 by the transmitting circuit
2 and the antenna 1.
[0070] FIG. 5 is a diagram showing use of channel frequencies. In
the field of the present mobile wireless communication, for channel
frequency assignment in VHF and UHF bands, channel widths of 25
kHz, 12.5 kHz and so on are being used. In the United States and
other countries, 25 kHz channels are presently used, but there is a
movement of band reduction to 12.5 kHz. Methods for reduction to
half of 12.5 kHz, i.e., 6.25 kHz, are being studied for application
in the near future. With respect to frequency bands other than the
220 MHZ frequency band, no practical use of single channels and no
practical communication system or method is known in which narrow
channels are set adjacent to each other for systematic use are
known.
[0071] Frequency allocation in this embodiment is such that the
conventional 25 kHz frequency band is divided into four narrower
bands. Of these frequency bands, referred to as frequencies f1, f2,
f3, and f4 below, the frequency bands f1 to f3 are used for "down
data communication" from the base stations to mobile terminals
while the frequency band f4 is used for "up data communication"
from mobile terminals to the upper base stations. In the
description of this embodiment, with respect to data transmitted to
the base station BA from the subscriber's terminal 227 via the
Internet network 20, transmission of the data from the base station
BA to one mobile terminal selected as desired is also referred to
as "down data".
[0072] As described above, the frequency band for one channel is
separated into frequencies in four narrower channels by dividing
the width of 25.5 kHz by 4, thus achieving effective use of
frequencies.
[0073] For use of narrower bands, the U.S. Federal Communications
Commission has formed a scheme of enabling use of frequencies in
6.25 kHz channels below 512 MHZ in the year of 2005. Similar
movements of frequency utilization are also seen in other
countries. Thus, the above-described use of frequencies in a
narrower band meets the present schemes for communication in
future.
[0074] FIG. 6 is a diagram showing the relationship between the
base stations and the channel setting with frequency bands f1 to f3
used for communication between the base stations.
[0075] While the embodiment has been described with respect to a
case where a plurality of base stations are provided. Table 1 shows
use of channel frequencies with respect to one base station.
1TABLE 1 Example of system (1) [with respect to one base station]
Base Mobile terminal Up trans- Receiving station mission repeater
trans- mission (Answerback) Trans- Mobile terminal Transmitting
Receiving mitting of f1 receives on f4 f4 and on f1 transmitting to
base station via wire circuit Trans- Mobile terminal Same as Same
as mitting of f2 receives above above on f2 Trans- Mobile terminal
Same as Same as mitting of f3 receives above above on f3 Repeat-
Group of mobile If there ing terminals cor- are many these
responding to transmis- f1 to f3 is sions from adapted or
terminals, suitable scan- the number receiving is of channels
performed. is increased.
[0076] When one base station first performs "down data"
transmission by using frequency f1, it transmits the same message
data to others on frequency f1. When a mobile terminal capable of
operating on frequency f1 receives the transmitted data, it
transmits an answer back signal on channel frequency f4. This
transmitted answerback signal is received by one of the receiving
repeaters to be transmitted as an answerback to the base station
via Internet network 20.
[0077] When the base station performs the next "down message"
transmission, it transmits data by using the next frequency f2.
When a mobile terminal capable of operating on frequency f2
receives the transmitted data, it transmits an answerback signal on
channel frequency f4. This transmitted answerback signal is
received by one of the receiving repeaters to be transmitted as an
answerback to the base station via Internet network 20.
[0078] When the base station performs a "down messages transmission
for the third time, it transmits data by using the third frequency
f3. When a mobile terminal capable of operating on frequency f3
receives the transmitted data, it transmits an answerback signal on
channel frequency f4. This transmitted answerback signal is
received by one of the receiving repeaters to be transmitted as an
answerback to the base station via Internet network 20.
[0079] When the base station further performs "down message"
transmission, it transmits data by using frequency f1 again. A
mobile terminal receiving the data transmits an answerback signal
on frequency f4.
[0080] This transmitting and receiving operation is repeated.
[0081] Table 2 shows a use of channel frequencies with respect to a
plurality of base stations provided as described above with
reference to the drawings.
2TABLE 2 Example of system (2) [with respect to a plurality of base
stations] Base station A Transmit- Each mobile Transmitting ting f1
terminal re- message data (key ceives f1 and answer- station) and
selects back on f4, Base station B Receiving errorless receiving by
f1, message in receiving retrans- received repeater, mitting f1
data sending to Base station C Receiving base station f1, via wire
retrans- circuit mitting f1 Transmitting and receiving are repeated
in the same manner when each of f2 and f3 is used. Mobile terminal
receives on f4, receiving repeater receives transmitted data, and
received data is sent to base station via wire circuit.
[0082] When base station BA first performs "down data transmission"
by using frequency f1, one of the other base stations receiving
this data transmits the same message data to the others on the same
frequency as frequency f1 on which the data has been received. Each
of the base stations receiving the data repeats this transmitting
and receiving operation. When a mobile terminal capable of
operating on frequency f1 receives the transmitted data, it
transmits an answerback signal on channel frequency f4. This
transmitted answerback signal is received by one of the receiving
repeaters to be transmitted as an answerback to base station BA via
Internet network 20.
[0083] The base station performing the next "down message"
transmission transmits data by using the next frequency f2. One of
the other base stations receiving this data transmits the same
message data to the others on the same frequency as frequency f2 on
which the data has been resolved. This transmitting and receiving
operation is repeated, when a mobile terminal capable of operating
on frequency f2 receives the transmitted data, it transmits an
answerback signal on channel frequency f4. This transmitted
answerback is received by one of the receiving repeaters to be
transmitted as an answerback to base station BA via Internet
network 20.
[0084] The base station performing a "down message" transmission
for the third time transmits data by using the third frequency f3.
One of the other base stations receiving this data transmits the
same message data to the others on the same frequency as frequency
f3 on which the data has been received. This transmitting and
receiving operation is repeated. When a mobile terminal capable of
operating on frequency f3 receives the transmitted data, it
transmits an answerback signal on channel frequency f4. This
transmitted answer back is received by one of the receiving
repeaters to be transmitted as an answerback to base station BA via
Internet network 20.
[0085] The base station further performs the "down message"
transmission by transmitting data by using frequency f1 again. One
of the other base stations receiving this data transmits the same
message data to the others on the same frequency as frequency f1 on
which the data has been received.
[0086] This transmitting and receiving operation is repeated.
[0087] In this embodiment, as described above, the channel
frequency is changed with a time shift each time down message
transmission is performed. Therefore, even if the communication
zones are close to each other and if messages are successively
transmitted, communication is free from mutual interference and no
jamming occurs.
[0088] In this embodiment, data is transmitted by one channel at a
time, which is different from a system such as an SMR system using
pair channels. Therefore, communication is free from mutual
interference, there is no need for a combiner or the like, and
circuits simple in configuration may suffice.
[0089] Further, in this embodiment, channel frequencies are used
with one antenna, so that there is no combination loss and
communication can be performed at high efficiency.
[0090] In this embodiment, data can be received with substantially
no multipath cancellation, fading or the like affecting the
data.
[0091] In this embodiment, no complicated communication protocols
are provided with respect to transmissions between the base
stations, and transmissions from the base stations to mobile
terminals (to receiving repeaters) and to the base stations. Only a
protocol of making each receiving unit respond is used. Since such
a simple communication protocol is used, the transmitters and
receivers can also be made simpler in circuit configuration.
[0092] FIG. 7 is a diagram showing the relationship between mobile
terminals and channel frequencies.
[0093] Mobile terminals use only up-transmission frequency f4.
Ordinarily, the transmission output power of mobile terminals in
low. Therefore, even if transmission is performed by using the same
frequency f4 over different zones, jamming cannot occur easily
between the different zones. If one frequency f4 is used, receiving
by each receiving repeater can be easily performed in this
embodiment of the present invention, therefore, one frequency f4 is
used in common for up message data transmission.
[0094] Needless to say, if a sufficiently wide frequency band
usable for up message transmission is assigned, or if the amount of
communication or the frequency communication is high, a plurality
of frequencies for up transmission can be set.
[0095] A description will now be given of the operation of the
embodiment of the present invention.
[0096] The base station BA transmits message data on frequency f1.
That is, a signal is formed by modulation with some data in the
modulator 3, and the signal carrying the data is transmitted in the
air by the transmitting circuit 2 and the antenna 1.
[0097] Message data transmitted from the base station BA is
received by the receiver RB of the base station BB located near the
base station BA. The base station BB forms a signal of the same
frequency f1 for the received message by modulation in the
modulator 3, and immediately transmits the signal in the air by the
transmitting circuit 2 and the antenna 1.
[0098] The message data transmitted from the base station BB is
received by the receiver RC of the base station BC located near the
base station BB. The base station BC immediately transmits the
received message on the same frequency. That is, the base station
BC forms a signal of the same frequency f1 for the received message
by modulation in the modulator 3, and immediately transmits the
signal in the air by the transmitting circuit 2 and the antenna
1.
[0099] The base station BA monitors the transmitted data from the
base station BB and the base station BC to confirm that it can
receive the message data sent out by it.
[0100] As illustrated in FIG. 1, zones formed as small or medium
zones are prescribed in urban and suburban areas, and receiving
repeaters are provided in the small or medium zones. One of
receiving repeaters RR placed in the small or medium zones receives
a transmitted electric wave in the f4 channel sent from a mobile
terminal.
[0101] As illustrated in FIG. 3, a data signal received by the
antenna 12 in one of the receiving repeaters RR placed in the small
or medium zones is input to the receiver 13 and is demodulated in
the receiver 13 to obtain data. Items of the received data are
stored in the memory in the data processor and memory section 14 in
the same order as the order in which they are input.
Simultaneously, the data items are grouped into packets each having
a certain data amount and are compressed. The data then undergoes
Transmission Control Protocol/Internet Protocol (TCP/IP) header
processing, is thereafter sent to the Internet provider 28 in the
Internet network 20 via the line interface 15 and the wire circuit
23, and is sent to the center unit CENT via the Internet network
20.
[0102] The data received by the center unit CENT is distributed to
the first to third memories 431 to 433 with respect to the kinds of
the data by the first data processor 41 in the data processor and
memory section 4 to be stored in the memories 431 to 433. The first
data processor 41 performs processing for decomposing the packets,
error correction and checking, processing for eliminating redundant
data, etc., and successively stores, in the memories 431 to 433,
data to be sent as an answerback for confirmation of incoming to
the message sender, i.e., mobile terminal P in this example, and
data to be sent to the subscriber's terminal or another mobile
terminal P to form queues.
[0103] As illustrated in FIG. 3, message data from the subscriber's
terminal 227 to the mobile terminal P is transmitted from the
Internet provider 26 via the wire circuit 21 connecting the
subscriber's terminal 227 and the Internet network 20, is sent to
the Internet network 20 via the Internet provider 26, and is set to
the center unit CENT via the Internet provider 27 and the wire
circuit 22. Such message data is stored in the corresponding one of
the memories 431 to 433 in the data processor and memory section 4
of the center unit CENT, is maintained in a wait state in a down
message queue, and is successively sent as down data to the mobile
terminal P via the transmitter TX by a method described below.
[0104] When a down message is sent from the subscriber's terminal
27 to the mobile terminal P, several incoming confirmation messages
from mobile terminal P may be sent by being combined and added to
the down message.
[0105] These message data groups are repeatedly transmitted by the
base stations BA to BC, as described above.
[0106] Reliable message communication can be achieved by repeatedly
sending the same message data from a plurality of base stations in
the above-described manner. Consequently, uniform communication
with reduced bit errors can be achieved in any urban zone, even
zones that are crowded with buildings and suburban zones where
buildings are scattered.
[0107] Such repeated transmissions of the same message data has a
diversity effect (attributable to signal redundancy) such that a
communication system can be established in which occurrence of bit
errors is limited, and which has improved reliability.
[0108] In the above-described embodiment, an Internet system is
incorporated as a wire circuit, so that existing communication and
data processing systems and communication apparatus can be used. As
a result, the entire system can be constructed at a comparatively
low cost and can be easily operated.
[0109] In the above-described embodiment, frequencies f1 to f3 in
four channel frequencies f1 to f4 in 6.25 kHz narrow bands obtained
by dividing a 25.5 kHz band are used for down data transmission,
while frequency f4 is used for up data transmission. However, use
of these channels is set as desired according to conditions. For
example, frequencies fl and f2 may be for down data transmission
while frequencies f3 and f4 are used for up data transmission.
[0110] Further, a frequency band wider than 25.5 kHz may be used by
being divided into a larger number of 6.25 kHz narrow bands.
[0111] The width of narrow bands used in accordance with the
present invention is not limited to 6.25 kHz.
[0112] In the above-described example of band setting, the width of
the narrow band is set to 6.25 kHz because the main theme relates
to transmission of message data.
[0113] If the communication system and the communication method of
the present invention are used for other applications, they may be
changed and modified in various ways from their forms as presented
in the embodiment described above.
[0114] While the embodiment of the present invention has been
described with respect to a preferred arrangement with reference to
the drawings, and while the configuration and operation of the
system, including Internet network 20, receiving repeaters and
subscriber's terminal 227, with which the invention will be carried
out, have been described, it is not always necessary to prepare
such apparatuses connected by wire circuits. Conversely, any other
apparatus may be added to the illustrated apparatus arrangement.
Such modifications may be easily made by those skilled in the
art.
[0115] According to the present invention, reliable message
transmission can be achieved by a simple method. That is, the same
data is repeatedly transmitted by changing the channel frequency
with a time shift each time a down message transmission is
performed. Therefore, even if the communication zones are close to
each other and if messages are successively transmitted,
communication is free from mutual interference and no jamming
occurs. As a result, a diversity effect can be achieved and a
stable and reliable communication system with reduced bit errors
can be established with respect to any urban zone, even zones
crowded with buildings, and suburban zones where buildings are
scattered.
[0116] According to the present invention, frequencies can be
effectively utilized.
[0117] According to the present invention, data is transmitted by
one channel at a time, so that communication is free from mutual
interference, there is no need for a combiner or the like, and
circuits simple in configuration may suffice.
[0118] Further, according to the present invention, channel
frequencies are used with one antenna, so that there is no
combination loss and communication can be performed at high
efficiency.
[0119] According to the present invention, a wire communication
system such as an Internet network is incorporated to enable use of
existing communication and data processing systems and
communication apparatuses. As a result, the entire system can be
constructed at a comparatively low cost and can be easily
operated.
[0120] In this embodiment, no complicated communication protocols
are provided with respect to transmission between the base
stations, and transmission from the base stations, to mobile
terminals (to receiving repeaters) and to the base stations. Only a
protocol of making each receiving unit respond is used. Since such
a simple communication protocol is used, the transmitters and
receivers can also be made more simple in circuit
configuration.
[0121] The mechanisms and processes set forth in the present
description may be implemented using a general purpose
microprocessor programmed according to the teachings in the present
specification, as will be appreciated to those skilled in the
relevant art(s). Appropriate software coating can readily be
prepared by skilled programmers based on the teachings of the
present disclosure, as will be apparent to those skilled in the
relevant art(s).
[0122] The present document is based on Japanese Patent Application
Hei 9-318123, filed in the Japanese Patent Office on Nov. 19, 1997,
the entire contents of which is incorporated herein by
reference.
[0123] Obviously, numerous modifications and variations of the
present invention are possible in light of the above teachings. It
is therefore to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described herein.
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