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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a time division communication system of
radio communication channels in a mobile communication system. More
particularly, the present invention relates to a time division
communication system of radio communication channels in a mobile
communication system in which one of many radio mobile stations within a
service area, to which radio channels are allocated, set up wireless
circuits connecting to radio base stations by using the allocated radio
channels, and when the first mobile stations are communicating with the
base stations through the wireless circuits, another mobile station
requests a communication with the base station currently engaging the
communication with the first mobile station, by using the same radio
channel as the first radio channel, a wireless circuit can be set up
between the second mobile station and the base station in a
transmitting/receiving diversity communication mode by the same radio
channel or another radio channel, without any adverse effect on the now
progressing communication between the first mobile station and the base
stations.
2. Description of Prior Art
A conventional mobile communication system has been employed in a land
mobile telephone system commercially serviced by NTT (Nihon Telephone and
Telegram Co., Ltd). The telephone system will be described with reference
to FIG. 16. A plurality of radio channels are allocated to a radio base
station 13, in order that it communicates with a number of mobile stations
15 carried on vehicles, which roam in a zone 14 as a service area. Each
mobile station 15 has a function to select one of the radio channels (this
function is called a multi-access). When the mobile station 15 desires to
communicate with the base station 13, the station 15 sends a control
signal to a wireless circuit control station 12 by way of the base station
13. The control station 12 determines radio channels used by many base
stations 13. In response to an instruction from the control station, the
mobile station 15 determines a speech channel number to be used for
communication, and communicates with a subscriber in a public telephone
network 10, through an exchange 11 including switches SW.
In the field of wireless communication, a transmitting/receiving diversity
technique is frequently used. Many diversity techniques have been known.
In a frequency diversity, at a transmitting point, a plurality of
transmitters simultaneously transmit the same signal at different
frequencies. At a remote receiving point, a plurality of receivers, tuned
to the transmitting frequencies, receives the transmitted signals, detect
them, and adds together the detected signals. In a transmission space
diversity, at a transmitting point, an output signal of a transmitter is
divided coupled with a plurality of antennae disposed at different
locations. These divided signals are transmitted from the antennae. At a
distant remote receiving point, the transmitted signals are received by a
single antenna, led to a receiver, and detected in the receiver. In a
receiving diversity, at a transmitting point, an output signal of a
transmitter is led to a single antenna, and is transmitted by the antenna.
At a remote receiving point, the signal is received by a plurality of
antennae disposed at different locations, and led to a receiver. After the
received signals are passed through a high (intermediate) frequency stage
or a detect stage, the received signals are added together.
In the transmitting/receiving diversity, amplitude modulation or angular
modulation is used for modulating a signal.
A communication system of the type in which the base station and the mobile
station use the same transmitting frequency, that is, the same radio
frequency is used as a transmitting/receiving frequency, is also used in
the digital mobile communication system.
In the communication system, if the number of radio channels for speech as
assigned to a base station is 10, those radio channels can be allocated to
communication requests by 10 number of mobile stations within a service
area. The communications of the base station and the mobile stations can
be done, while being free from radio interference. For an 11th call
originating request generated by a mobile station, the base station cannot
originate a call (call loss) because there is no radio channel assigned to
the mobile station. The above description of problem relates to the case
where the radio channel is used for transmitting an analog signal. The
same problem is involved in the communication system using a voice signal
subjected to digital modulation process, and the system of the single
channel per carrier (SCPC) type in which a telephone (communication)
signal is transferred by a single carrier wave.
Further, in the system using only assigned radio channels, the band width
of the signal is fixed. Accordingly, it is impossible to transmit a signal
whose band width is broader than that of the assigned channel.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a mobile
communication system in which a plurality of radio mobile stations can
more flexibly communicate with at least one radio base station by using an
increased number of communication paths, while successfully solving the
problem that a maximum number of communications is limited to the number
of radio channels assigned to the base station, and the problem of
limiting the frequency band of the transmission signal to within the
frequency band of the assigned radio channel.
To achieve the above object, there is provided a mobile communication
system comprising:
a plurality of radio base stations each with a radio transmitter;
at least one mobile station engaging a communication while moving service
areas covered by the plurality of radio base stations,
the mobile station including a radio receiving circuit with a receiving
mixer, a radio transmitting circuit with a transmitting mixer, switch
receiving means including frequency synthesizers being capable of
selectively receiving signals of two channels by applying two frequencies
to the receiving mixer of the radio receiving circuit, switch transmitting
means including synthesizers being capable of selectively transmitting
signals of two channels by applying two frequencies to the transmitting
mixer of the radio transmitting circuit,
the mobile station in which, a transmitting signal (base band signal) is
segmented at predetermined time intervals and those segmented signals are
stored into a memory circuit, the stored signals are read out of the
memory circuit through predetermined time slots and at a high speed that
is "n" times higher than when those signals are stored, a carrier wave is
angle modulated or amplitude modulated by the signal contained in the time
slot, a radio receiving circuit with a receiving mixer, and a radio
transmitting circuit with a transmitting mixer, the radio receiving and
transmitting circuits forming a pair of communication parties, which are
contained in the mobile station and the base station for the transmission
and reception which are interruptive with respect to time, a switch
circuit is provided for a synthesizer to apply a signal to the receiving
mixer of the radio receiving circuit and another synthesizer to apply a
signal to the transmitting mixer of the radio transmitting circuit, a
method is employed in which the output signals of the synthesizers are
interrupted, the interrupting operations of the output signals in the
transmitting circuit side are synchronized with those in the receiving
circuit side, and the interruptive transmission and reception in the base
station is synchronized with those in the mobile station as a counter part
of the paired communication parties, in the receiving side, in order to
pick up only the signal contained in the predetermined time slot,
transmitted signals are received by opening and closing the radio
receiving circuit, and are demodulated and stored into the memory circuit,
and the signal are read out of the memory at a low speed that is 1/n times
slower than when the signals are stored, in the base station, speech path
control means for setting up a speech path between the base station and a
predetermined mobile station by using a predetermined time slot, is
provided; and a gateway exchange for connecting the base stations and a
public telephone network, which enables the base band signal as the
original signal as transmitted to be reproduced in the base stations and
the mobile stations.
With such an arrangement, even when the radio channels assigned to the
system are all used, if an idle time slot being not yet used is present in
the time slots arrayed in time division manner in each radio channel, the
base station can originate a call for a mobile station which additionally
requests the base station to originate a call. Also for a mobile station
which is present in a radio zone adjacent to the radio zone in which the
base station is located and now engages the communication with the base
station, the base station can continue the communication. Further, a
mobile station, which now engages the communication with one base station,
can communicate with another radio base station located near the mobile
station in a diversity mode. When the transmission of a broad band signal
is requested, such a signal can be transmitted by using a necessary number
of time slots if idle time slots are present. By allocating time slots of
one channel that can be used, to a plurality of base stations, one channel
can be used commonly by the plurality of base stations. Thus, in the
mobile communication system according to the present invention, the
frequency utilization efficiency is remarkably improved.
In a mobile communication system including a base station and a number of
mobile stations present in a service area of the base station, to enable
an appropriate number of mobile stations to communicate with the base
station, one radio channel is segmented into a series of time slots in a
time divisional manner. One of the time slots is selected for
communication. In a situation that when one mobile station is
communicating with a base station, another mobile station sends a
communication request signal to the base station. In such a situation, an
idle time slot of those time slots of the radio channel being currently
used is allotted to the mobile station requesting a communication anew. By
using the idle time slot, the new mobile station can communicate with the
base station, Accordingly, a plurality of communications can concurrently
be carried out without any radio interference among them and within each
communication.
For example, when a base station is transmitting a signal by using a given
time slot, a mobile station exclusively receives a signal as transmitted
by using the time slot. Alternately, when the mobile station sends a
signal by using a given time slot, the base station exclusively receives
the signal as transmitted from the mobile station by the time slot. Thus,
a single radio channel can be used for both the transmission and the
reception.
When one base station is communicating with a mobile station by using one
time slot in a channel (one time slot of an old channel), it communicates
with another base station, which satisfies a preset communication quality,
by using one time slot of the same channel or another channel (one time
slot of a new channel), thereby to maintain and improve a communication
quality. For a terminal device using a broad band signal, a plurality of
time slots are used for transmitting the broad band signal. A
communication service by the mobile communication system is improved,
accordingly.
Different time slots of one radio channel are assigned to base stations
adjacent to each other. Accordingly, the same radio channel can be used
for the adjacent base stations without any radio interference.
Accordingly, the utilization of radio channels is remarkably improved.
In a communication system (which is called a Ping-Pong transmission, and
used in a conventional digital communication system) of the type in which
the base station and the mobile station use the same transmission
frequency, but different transmission timings, when the transmission speed
becomes high, e.g., approximately 200 kbps, an average error bit rate is
remarkably increased due to the multipath propagation wave. In the present
invention, the increasing of the error bit rate is alleviated.
Accordingly, a mobile communication system with high performance can be
realized.
Other objects, advantages and features of the present invention will be
apparent from the following description in connection with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a diagram showing an arrangement of a gateway exchange contained
in a mobile communication system according to the present invention, and
the connection among the gateway exchange, a public telephone network, and
base stations;
FIG. 1B-1 shows a circuit arrangement of a mobile station used in the
mobile communication system according to the present invention;
FIG. 1B-2 shows a circuit arrangement of a radio receiving circuit in FIG.
1B-1;
FIG. 1C shows a circuit arrangement of a base station used in the mobile
communication system according to the present invention;
FIGS. 1D, 1E, and 1F show circuit arrangements of other mobile stations
that can be used in the mobile communication system according to the
present invention;
FIG. 2A shows a time slot structure useful in explaining time slots used in
the mobile communication system according to the present invention;
FIG. 2B shows waveforms of transmission and receiving signals of a base
station, which contain time slots;
FIGS. 2C and 2D show time slot structures useful in explaining a channel
switching operation;
FIGS. 2E(a) and 2E(b) show a spectral diagram and a circuit arrangement,
which are useful in explaining a structure of a control signal used in the
present invention;
FIGS. 2F through 2K show time slot arrangements useful in explaining other
time slots used for the mobile communication system according to the
present invention;
FIGS. 3A and 3B are spectral diagrams showing spectra of a speech signal
and a control signal;
FIGS. 4A and 4B show a flowchart showing a flow of a location registration
operation of the mobile communication system according to the present
invention;
FIGS. 5A through 5C cooperate to show a flowchart showing a flow of a call
originating operation of the mobile communication system according to the
present invention;
FIGS. 6A through 6D cooperate to show a flowchart showing a flow of a call
terminating operation of the mobile communication system according to the
present invention;
FIGS. 7A through 7D cooperate to show a flowchart showing a flow of a
channel switching operation of the mobile communication system according
to the present invention;
FIGS. 8A through 8D cooperate to show a flowchart showing a flow of a
transmitting/receiving diversity communication in the mobile communication
system according to the present invention;
FIG. 9 shows a table comparatively showing the effects of the
transmitting/receiving diversity communication in the conventional mobile
communication system and the mobile communication system according to the
present invention;
FIG. 10 is a spectral diagram showing a radio interference with the
adjacent channels in the mobile communication system according to the
present invention;
FIG. 11A is a schematic illustration of a microcell system to which the
present invention is applied; FIG. 11B shows a schematic illustration of a
microcell system to which a time slot allocation according to the present
invention is applied;,
FIGS. 12A and 12B show timing charts useful in explaining delay time
generated in the signal compression/expansion process in the mobile
communication system according to the present invention;
FIG. 13(a) and 13(b) show spectral diagrams for explaining necessary band
widths of the conventional mobile communication system and the mobile
communication system according to the present invention;
FIGS. 14A and 14B cooperate to form a flowchart showing a flow of a
location registration operation when an intra-frame time slot allocation
according to the present invention is used;
FIGS. 15A to 15C cooperate to form a flowchart showing a flow of a call
originating operation when an intra-frame time slot allocation according
to the present invention is used; and
FIG. 16 shows a schematic illustration for explaining a conventional mobile
communication system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A mobile communication system based on the time division communication
according to an embodiment of the present invention is configured as shown
in FIGS. 1A, 1B-1, 1B-2, and 1C. The present mobile communication system
employs a small zone architecture, more exactly a so-called cellular or
microcell system in which each zone is extremely small, within 1 km, as
described in paper entitled "A Proposal of Time-Division, Time-Compressed
Multiplexing FM Mobile Radio System" written by Sadao Itoh, SHINGAKU GIHOH
(Technical Comittee Report of the Institute of Electronics Information and
Communication Engineers), CS 86-88, Nov. 1987. In the microcell system,
the radio zones overlap, and one radio zone frequently serves as another,
adjacent radio zone.
In FIG. 1A, reference numeral 10 designates a general public switched
telephone network (PSTN); 11 an exchange closer to the telephone network
10; 20 a gateway exchange for switching the exchange 11 with a radio
system. The gateway exchange 20 controls a plurality of radio base
stations 30 and a number of mobile stations in order to change channels
one to another when radio channel assignment and release, and zone shift
are executed. The gateway exchange 20 is made up of a communication
controller 21 for controlling "n" number of radio base stations 30-1 to
30-n, an ID memory 24 for discriminating an identification (ID) number of
each mobile station, an S/N monitor 25 for monitoring communication
quality when the radio stations 30-1 to 30-n receive radio waves from
mobile stations, and a group of switches 23 necessary for switching the
communication lines between the exchange 11 and the respective radio
stations 30-1 to 30-n under control of the communication controller 21.
For each of illustration of the switch group 23, there are illustrated
only three incoming lines connecting to the exchange 11, and outgoing
lines of n.times.m for wirelessly transmitting to the radio stations 30-1
to 30-n, communication signals 22-1-1 to 22-1-m, 22-2-1 to 22-2-m, . . . ,
22-n-1 to 22-n-m.
The radio base station 30 is made up a switch group for speech paths
serving as an interface with the gateway exchange 20, a speech path
controller for controlling the switch group, a circuit for signal speed
(pitch) conversion of an ID discrimination memory signal, a circuit for
assignment and select of time slots, a controller, a receiver/transmitter
for a plurality of radio channels. The radio base station 30 sets up and
releases radio channels, and further includes a transmitting/receiving
circuit for transmitting and receiving radio signals to and from a number
of mobile stations.
Between the gateway exchange 20 and the radio station 30, transmission
lines are provided for transmitting communication signals 22-1 to 22-m
containing speech signals of speech channels CH1 to CHm and control
signals.
A circuit arrangement of the mobile station 100 for making a communication
with the radio base stations 30-1 to 30-n is shown in FIG. 1B-1. The
communication signal containing the speech signal and the control signal
as is received by an antenna section, enters a receiver 135 including a
receiving mixer 136 and a receiving section 137. The output signal of the
receiver 135 is input to signal speed (pitch) restoring circuits 138-1 and
138-2, and a clock regenerator 141. The regenerator 141 regenerates a
clock signal on the basis of the received signal, and delivers it to the
signal speed restoring circuits 138-1 and 138-2, controller 140, timing
generator 142, and signal speed (pitch) converting circuits 131-1 and
132-2.
The signal speed restoring circuits 138-1 and 138-2 restore speeds (in the
case of an analog signal, pitches) of two communication signals as
compressed and segmented in two time slots in the received signals of two
channels, thereby to form a continuous signal. The continuous signal thus
formed is subjected to a mixing process in a signal mixer 152. The output
signal of the signal mixer 152 is delivered to a telephone section 101,
speech signal monitor 157, and ID data verification/memory 182.
An output signal of the telephone section 101 is divided into two signals
by a signal divider 139. The divided signals are applied to signal speed
converting circuits 131-1 and 131-2, respectively. In the converting
circuits, the communication signals are segmented at predetermined time
intervals to increase (compress the signals) the signal speed (in the case
of the analog signal, pitches). The output signals of the signal speed
converting circuits are applied to a transmitter 132 including a
transmitting mixer 133 and a transmitting section 134. The transmitting
signals are transmitted by using two time slots from the antenna section,
The speech quality monitor 157, which receives the output signal of the
signal mixer 152, constantly monitors a speech quality of the speech
signal under communication. When detecting a degradation of the speech
quality, the monitor transfers the degradation to the controller 140. The
ID data verification/memory 182 stores ID data of the mobile station per
se, and recognizes a radio zone in which the mobile station is now
present, and stores the zone. An interference detector 162 monitors radio
interference under communication. When the radio interference exceeds a
predetermined level, the interference detector 162 sends the excessive
interference to the controller 140.
The timing generator 142 generates timing signals on the basis a clock
signal from the clock regenerator 141 and a control signal from the clock
controller 140, and delivers them to a transmitting/receiving interrupt
controller 123, the signal speed converting circuits 131-1 and 131-2, and
the signal speed restoring circuits 138-1 and 138-2.
The mobile station 100 further includes synthesizers 121-1 to 121-4 for
enabling simultaneous transmission and reception of two channels, select
switches 122-1 and 122-2, the transmitting/receiving interrupt controller
123 for operating the switches 122-1 and 122-2, and the timing generator
142. The synthesizers 121-1 to 121-4, the transmitting/receiving interrupt
controller 123, and the timing generator 142 are controlled by the
controller 140. A reference frequency is applied from a reference crystal
oscillator 120 to the synthesizers 121-1 to 121-4. With such an
arrangement, the mobile station can communicate with the plurality of
radio base stations 30 by using two channels.
FIG. 1B-2 shows an arrangement of an internal circuit of the radio
receiving circuit 135. A signal as received by the antenna section is
applied to the receiving mixer 136, which receives a local oscillator
frequency through the switch 122-1 from the synthesizer 121-1. The output
signal of the receiving mixer 136 is applied to an intermediate frequency
IIF) amplifier 143. The signal as amplified by the IF amplifier 143 is
applied to a gate circuit 144 and the clock regenerator 141. The gate
circuit 144 functions to pick up only signals of desired time slots
without any interference from other time slots. The output signal of the
gate circuit 144 is demodulated by a discriminator 145, and applied
through a gate circuit 146 to the signal speed restoring circuit 138. The
gate circuit 146 removes transient components of a waveform after
demodulation.
FIG. 1C shows an arrangement of the radio base station 30. The
communication signals 22-1 to 22-m of "m" channels are coupled with a
signal processor 31 as an interface by way of transmission paths between
the base station 30 and the gateway exchange 20.
In operation, the communication signals 22-1 to 22-m coming through the
gateway exchange 20 reaches the signal processor 31 in the radio base
station 30. The signal processor 31 includes an amplifier for compensating
for a transmission loss. The signal processor has many functions; function
for a transmitting/receiving diversity using time slots of two or more,
function to divide the signal for a plurality of radio
transmitting/receiving sections, and function to make the 2-4 wires
conversion when the transit trunk consists of 2 wires. That is, the signal
processor executes mixing and separation of the input and output signals.
The signals from the gateway exchange 20 are applied to a signal speed
converting circuit group 51-1 containing a number of signal speed
converting circuits 51- 1-1 to 51-1-m and another signal speed converting
circuit group 51-2, through a switch group 83. The switch group 83
includes a group of switches SWR1 containing SWR 1-1-1, SWR 1-1-2, . . . ,
SWR 1-1-m, SWR 1-2-1, SWR 1-2-2, . . . , SWR 1-2-m, . . . , . . . , SWR
1-n-1, SWR 1-n-2, . . . , SWR 1-n-m, a group of switches SWR2 containing a
number of like switches, a group of another type of switches SWT1
containing SWT 1-1-1, SWT 1-1-2, SWT 1-1-m, SWT 1-2-1, SWT 1-2-2, . . . ,
SWT 1-2-m, . . . , . . . , SWT 1-n-1, SWT 1-n-2, . . . , SWT 1-n-m, and a
group of switches SWT2 containing a number of like switches.
The output signals of a signal restoring circuit group 38-1 including
signal restoring circuits 38-1-1 to 38-1-m, and another signal speed
restoring circuit group 38-2, are applied through the switch group 83 to
the signal processor 31. Those signals are transmitted as communication
signals 22-1 to 22-m from the signal processor 31 through the same
transmission paths as those for the input signals to the gateway exchange
20. The switches in the switch group 83 are categorized into two types,
switches for transmission SWTl and SWT2, and switches for reception SWR1
and SWR2. Both types of switches operate to effect the intended functions
of the switch group 83 under control of the speech path controller 81, and
consequently allows the transmitting/receiving diversity operation.
The ID memory 82 is used for discriminating an ID of the mobile station
100, and storing the registered ID. The speech path controller 81 receives
instructions from the controller 40 and operates the switch group 83,
thereby to exercise the controls on the speech path. Further, the speech
path controller 81 sends data to the controller 40, and control request
signals to the same. The signals from the gateway exchange pass through
the switch group 83, and reach the signal speed converting circuit group
51-1 including many speed converting circuits 51-1-1 to 51-1-m, and the
speed converting circuit group 51-2. In those groups, the signals are
subjected to the speed (pitch) conversion at predetermined time intervals.
The signals transmitted from the radio base station 30 to the gateway
exchange 20 are input through the switch group 83 to the signal processor
31, after the output signals of the radio receiving circuits 35-1 to 35-2
are input through signal select circuit groups 39-1 and 39-2 to the signal
speed restoring circuit groups 38-1 and 38-2 where those signals are
subjected to the speed (pitch) conversion.
The speech signals or the control signals output from the radio receiving
circuits 35-1 and 35-2 are input to the signal select circuit groups 39-1
and 39-2 each including signal select circuits 39-1-1 to 39-1-m for
selecting the signals for each time slot. In the signal select circuit
groups 39-1 and 39-2, the speech signals are separated corresponding to
time slots contained in the two radio channels, e.g., channels CH1 and
CH2, as received by the radio receiving circuits 35-1 and 35-2. The output
signals of the signal select circuit groups are applied to the signal
speed restoring circuit groups 38-1 and 38-2 each including many signal
speed restoring circuits 38-1-1 to 38- 1-n as provided corresponding to
the respective speech signals. The signal speed restoring circuit groups
restore the speeds of the signals. The output signals of the signal speed
restoring circuit groups are applied through the switch group 83 to the
signal processor 31. In the processor, those are subjected to the 2-4
wires conversion, and then are output to the gateway exchange 20, in the
form of communication signals 22-1 to 22-m.
A circuit arrangement of each radio receiving circuit 35-1 and 35-2 is the
same as that of the radio receiving circuit 135 in the mobile station 100
shown in FIG. 1B-2.
The functions of the signal speed converting circuit groups 51-1 and 51-2
will be described.
A time length of a signal can be compressed in a manner that an input
signal as segmented at fixed time intervals, such as a voice signal and a
control signal, are stored in a memory, and the signal is read out of the
memory at speed different from that when it is stored, for example, speed
15 times as high as the speed of the signal when it is stored. The
principle of the signal speed converting circuit group 51 resembles that
of the case where a voice recorded in a tape recorder is reproduced at a
high speed. Practically, a CCD (charge coupled device) and BBD (bucket
brigade device) are available for the signal speed converting circuit
group 51. Further, a memory device may be used which is used in a
television receiver or a tape recorder to expand or compress the time axis
of conversation. For the details, reference is made to paper entitled
"Tape Recorder to Compress/Expand the Time Axis of Conversation" written
by Kosaka et. al in NIKKEI ELECTRONICS, Jul. 26, 1976, pp. 92 to 133.
A circuitry using a CCD or BBD as for the signal speed converting circuit
groups 51-1 and 51-2, as referred to in the above article, is
straightforwardly applied to the signal speed restoring circuit groups
38-1 and 38-2. In this case, upon receipt of a timing signal from the
timing generator 42, which generates the timing signal on the basis of a
clock signal from the clock generator 41 and a control signal from the
controller 40, the signal restoring circuit groups decreases the signal
read speed below the signal write speed.
The control or speech signals as transferred through the signal processor
31 from the gateway exchange 20 are applied to the signal speed converting
circuit groups 51-1 and 51-2, where the signals are subjected to the speed
(pitch) conversion process. Then, the signals are applied to signal
allocation circuit groups 52-1 and 52-2 where the signals are allocated in
compliance with the time slot. The signal allocation circuit groups 52-1
and 52-2 are of the buffer memory type, and each store one frame of each
of the high speed signals output from the signal speed converting circuit
groups 51-1 and 51-2. On the basis of the timing data as generated from
the timing generator 42 by an instruction from the controller 40, the
signal data are read out of the buffer memories, and are transferred to
radio transmitting circuits 32-1 and 32-2. As a result, the communication
data when considered as speech signals are arranged in time sequential
order, not in an overlapping fashion. The communication data, when filled
with control or speech signals to be given later, takes a form like a
consecutive signals waveform.
Signal formats when the signals are compressed will be described with
reference to FIGS. 2A and 2B.
The output signals of the signal speed converting circuits 51-1 and 51-2
are input to the signal allocation circuit groups 52-1 and 52-2 where the
signals are allocated to time slots in predetermined order. In FIG. 2A(a),
the downward (abbrevates as down hereafter) communication signals
(abbrevates as SP) as speed converted are allotted to time slots SD1, SD2,
SDn, and output from the radio transmitting circuits 32-1 and 32-2
(generally designated by 32 in the figure).
As shown, one time slot contains a synchronous (abbrevates as sync) signal
and a speech signal and/or a control signal. When the speech signal is not
contained, the slot contains a sync signal as applied in the speech
controller 81, and an idle slot signal in the speech signal part. In some
systems, no signal is present in the speech signal part of the time slot.
Thus, a signal in which one frame consists of the time slots SD1 to SDn is
applied to the modulator in each of the radio transmitting circuits 32-1
and 32-2.
A multiplexed signal as time sequentially arranged is amplitude-modulated
or angle-modulated in each transmitting circuit 32, and then is
transmitted to air from the antenna section.
In some systems, the radio signal is transmitted only for the time slots
containing the control signal or speech signal, while no radio signal
including a carrier wave is transmitter for other time slots. As for such
systems, description will be given later in "(6) Time Slot Allocation
within One Frame". The radio transmitting circuit 32 in the radio base
station 30 in such a system may be substantially the same as the radio
transmitting circuit 132 in the radio base station 100 shown in FIG. 1B-1,
for example.
A frequency within or outside the band with of the speech signal may be
used for transmitting control signals between the radio base station 30
and the mobile station when the telephone section calls or is called,
which the control signal transmission precedes to the speech
communication. This is illustrated in FIG. 3A. As shown in FIG. 3A(a), the
frequency used for transmitting the control signals is located outside the
frequency band, viz., at 250 Hz one the lower frequency side of the
frequency band or at 3850 Hz on the higher frequency side. The frequency
outside the frequency band is used for sending the control signal when the
speech communication progresses, e.g., when in- communication handover or
the diversity is desired to be applied.
These control signals are formed in the controller 40 or relaying or
converting the control signals from the gateway exchange 20 or the speech
path controller 81 by the controller 40.
The control signals originating from the mobile station 100 are received by
the radio receiving circuits 35-1 and 35-2, and appropriately processed by
the controller 40, and if required, are transferred to the speech path
controller 81 and the gateway exchange 20.
In FIG. 3A(b), the frequency for transmitting the control signals is
located within the frequency band, and is used at the time of call or
being called.
While in the above description, the control signals are tone signals, the
number of tone signals may be increased or the tone signals may be
modulated into a sub-carrier signal. In this case, many types of tone
signals may be sent at high speed.
In the above description, the analog control signals are treated. If
required, digital data signals may be used for the control signals. In
this case, the speech signal is also digitized. Both the control and
speech digital signals are time division multiplexed before transmitted. A
circuit arrangement to realize this is shown in FIG. 2E(b). As shown, an
analog voice signal is digitized by a digital encoding circuit 91, and it
is multiplexed with a data signal in a multiplex/converter circuit 92. The
multiplexed signal is applied to the modulator contained in the radio
transmitting circuit 32.
The multiplexed signal is received by a receiver, and is subjected to a
reverse procedure of the procedure of FIG. 2E(b), in the demodulator of
the receiver. Through the reverse procedure, the speech signal and the
control signal are separately derived from the multiplexed signal.
A signal sent from the mobile station 100 is received by the antenna
section of the radio base station 30, and is applied to the radio
receiving circuits 35 (35-1 and 35-2). This upward (abbrevates as up
hereafter) signal (abbrevates as SU) is shown as a model in FIG. 2A(b). In
the figure, time slots SU1, SU2, . . . , SUn indicate the signals
transmitted from the mobile stations 100-1, 100-2, . . . , 100- n to the
radio base station 30 (e.g., 30-1). Each of the time slots SU1, SU2, . . .
, SUn consists of a sync signal and/or a speech signal as illustrated in
the lower left portion in FIG. 2A(b). The sync signal is omissible when a
distance between the radio base station 30 and the mobile station 100 or
if some specific signal speeds are used. A carrier wave of the up radio
signal within each time slot is as shown in FIG. 2B(c).
Of the input signal arriving at the radio base station 30, the control
signal is straightforwardly applied from the radio receiving circuits 35-1
and 35-2 to the controller 40. At some specific speed converting ratios,
after the speech signal is subjected to a similar processing, it may be
applied from the outputs of the signal speed restoring circuit groups 38-1
and 38-2 to the controller 40. The speech signal is applied to the signal
select circuit groups 39-1 and 39-2. A timing signal as generated by the
timing generator 42 in accordance with an instruction of the control
signal from the controller 40, is applied to the signal select circuit
groups 39-1 and 39-2. At the timing of the timing signal, each signal
select circuit group separates the time slot signals into a sync signal, a
control signal and a speech signal for each time slot. These signals are
applied to the signal speed restoring circuit groups 38-1 and 38-2. These
circuits make reverse operations of those by the speed converting circuits
131-1 and 131-2 (FIG. 1B-1) in the mobile station 100. Through the reverse
converting operation, the replica of the original signals are faithfully
reproduced, and transferred to the gateway exchange 20.
How the signals propagate in a signal space will be described in connection
with necessary transmission frequency band, and radio channels adjacent to
it.
As shown in FIG. 1C, the control signal from the controller 40, together
with the output signals of the signal allocation circuit groups 52-1 and
52-2, is applied to the radio transmitting circuits 32-1 and 32-2. At some
specific signal converting ratios, after the control signal is subjected
to a similar processing to that of the speech signal, it may be applied
from the outputs of the signal speed allocation circuit groups 52-1 and
52-2 to the radio transmitting circuits 32-1 and 32-2.
The mobile station 100 also employs the circuit arrangement necessary for
realizing one of the functions of the radio base station 30 that is to
receive the the two speech signals as transmitted by using two time slots
as shown in FIG. 1B-1. An original signal, e.g., a speech signal (0.3 kHz
to 3.0 kHz), after passing through the signal speed converting circuit
group 51 (FIG. 1C), has a frequency distribution as shown in FIG. 3B. As
already described, where the speed of the voice signal is increased to be
speed 15 times as high as the original one, the frequency distribution of
the speech signal is expanded to be 4.5 kHz to 34 kHz as shown in FIG. 3B.
In the case illustrated, the control signal, together with the speech
signal, is transferred by using a lower side band of the speech signal.
It is assumed now that a control signal (0.2 to 4.0 kHz) and a speech
signal (4.5 to 45 kHz) denoted as SD1 are contained in a time slot SD1,
for example. The same thing is true for other time slots SD2 to SDn.
As a generalization, a control signal (0.2 to 4.0 kHz) and a communication
signal CHi (4.5 to 45 kHz) are contained in a time slot SDi (i=2, 3, . . .
, n). Within each time slot, the signals are arranged time sequentially.
Accordingly, there never occurs such a situation that the signals within a
plurality of the time slots will simultaneously be applied to the radio
transmitting circuits 32-1 and 32-2.
When those speech signals, together with the control signal, are applied to
the angle modulator contained in each radio transmitting circuit 32-1 and
32-2, at least the following frequency band is required to transmit those
signals as modulated
fc.+-.45 kHz,
where fc is the frequency of a carrier wave. In case where a plurality of
radio channels are provided in this system, the minimum frequency interval
among those channels limits increase of the signal speed by the signal
speed converting circuit groups 51-1 and 51-2 to a certain value. The
following inequality must hold between the frequency interval freg among
the radio channels and a maximum signal speed fH of the voice signal when
the signal speed is increased
freq>2fH.
The voice signal is digitized at the rate of usually about 16 to 64 kb/s.
Accordingly, when a scale of the abscissa in FIG. 3B which depicts the
frequency distribution of the analog signal is applied to the frequency
distribution of the digital signal, the scale must be expanded by a figure
up one place. Also in this case, the above inequality holds.
The control signal as transmitted from the mobile station 100 to the radio
base station 30 is input to the radio receiving circuits 35-1 and 35-2.
The output signals of the radio receiving circuits 35-1 and 35-2 are
applied to the controller 40, and also to the signal speed restoring
circuit groups 38-1 and 38-2 by way of the signal select circuit groups
39-1 and 39-2. In the signal speed restoring circuit groups, the control
signals are subjected to the speed conversion exactly inverse to that of
the transmission side (signal speed conversion from high speed to low
speed). The converted signal speed is equal to that in the public switched
telephone network 10. Then, the signal speed converted control signal is
applied through the signal processor 31 to the gateway exchange 20.
Turning now to FIG. 1D, there is shown another embodiment of the mobile
station 100. In this embodiment, the mobile station is denoted as 100B.
The instant mobile station 100B is different from that 100 in that a
couple of radio transmitting circuits 132-1 and 132-2, and a couple of
radio receiving circuits 135-1 and 135-2 are provided, and the output
signals of the synthesizers 121-1 to 121-4 are applied to those circuits
by way of switches 124-1 to 124-4 that are turned on and off under control
of a transmitting/receiving interrupt controller 123B. The
transmitting/receiving interrupt controller 123B opens and closes the
switches 124-1 to 124-4 in accordance with an instruction from the
controller 140B. With such an arrangement, the mobile station 100B will be
free from the radio interference. A transmitting/receiving diversity can
always be carried out between the mobile station and one radio base
station.
FIG. 1E shows yet another embodiment 100C of the mobile station 100. The
difference of the instant embodiment from the mobile station 100 lies in
that a signal speed restoring circuit 138 and a speech converting circuit
131, and a couple of synthesizers 121-1 and 121-3 for transmitting and
receiving use are provided, and that the signals of given time slots can
be transmitted and received through switches 122-1 and 122-2, which are
operated under control of a transmitting/receiving interrupt controller
123C operable by an instruction from the controller 140. Therefore, a
transmitting/receiving diversity can be carried out in this embodiment.
For simplifying the circuit arrangement, only one set of the signal speed
restoring circuit 138 and the signal speed converting circuit 131 is used,
and the signal mixer 152 and the signal divider 139 are omitted.
FIG. 1F shows still another embodiment 100D of the mobile station 100. The
difference of the instant embodiment from the mobile station 100 shown in
FIG. 1B lies in that the synthesizers 121-1 and 121-2 are used for both
the transmitting and receiving, and the mobile station does not receive
the signals in a transmission mode, and does not send the signals in a
receiving mode by the switches 122-1 and 122-2, which are operated under
control of a transmitting/receiving interrupt controller 123D operable by
an instruction from the controller 140D. With such an arrangement, the
same radio frequency can be used for sending and receiving signals.
Various operation of the mobile communication system thus arranged will be
described in the order as given below. It is believed that the description
on the operations to follow will theoretically prove excellent utility of
the present invention. In the description, speech signals will first be
used, and then non-telephone signals will be used.
(1) Location Registration
(2) Call Originating Operation
(3) Call Incoming Operation
(4) Handover
(5) Transmitting/Receiving Diversity Between Plurality Base Stations and a
Mobile Station
(6) Time Slot Allocation within One Frame
(7) Comparison of the Diversity Effects by the Invention and by Prior Art
(8) Theoretical Description of the Invention
(I) Adjacent Channels Interference
(II) Intra-channel Interference
(III) Co-Channel Interference
(IV) Removal of Pulsative Noise in Signal Reception
(V) Delay Time Effect of Transmission Signal
(VI) Calculation of Effective Frequency Utilization
(9) Application of the Invention to a Communication System using a
Non-telephone Signal (Broad Band Signal) Other Than a Speech Signal
(10) Application to the Invention to a Mobile Communication System Using
the Same Radio Frequency for the Signal Transmission Between a Base
Station and Mobile Stations
(1) Location Registration
Any one of mobile stations shown in FIGS. 1B-1, 1B-2, 1D, and 1E is
available for the mobile station 100 in the mobile communication system
according to the present invention. In the description on the location
storage that follows, the mobile station 100C shown in FIG. 1E will be
used. Other mobile stations of FIG. 1B-1 and 1B-2, for example, may be
considered to have substantially the same arrangement as that of FIG. 1E,
if only the synthesizers 121-1 and 121-3 are operating, while the
remaining synthesizers 121-2 and 121-4 are rest. The same status is true
for the mobile station 100B of FIG. 1D, if only the combination of the
receiving section 135-1 and the transmitting section 132-1 are operating,
while the receiving section 135-2 and the transmitting section 132-2 are
rest. For this reason, the mobile stations 100, 100B and 100D will be
designated representatively by reference numeral 100.
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