U.S. patent application number 10/569627 was filed with the patent office on 2007-07-19 for polling method and vehicle search method in digital radio communication system.
Invention is credited to Kin'ichi Higure, Yuzo Hiraki, Masayuki Kanazawa, Minoru Sakaihori.
Application Number | 20070165591 10/569627 |
Document ID | / |
Family ID | 34277631 |
Filed Date | 2007-07-19 |
United States Patent
Application |
20070165591 |
Kind Code |
A1 |
Higure; Kin'ichi ; et
al. |
July 19, 2007 |
Polling method and vehicle search method in digital radio
communication system
Abstract
The present invention provides a polling method in a radio
digital communication system making it possible to shorten time
required for polling without causing increase in an error rate and
to efficiently manage and administrate communications. In a digital
radio communication system for collecting information from a
plurality of terminal stations by polling, a polling response
signal to be transmitted from each terminal station to a base
station has a frame format constructed of a one-frame in which a
cyclic bit pattern is placed at a leading end of the frame
format.
Inventors: |
Higure; Kin'ichi; (Kodaira,
JP) ; Kanazawa; Masayuki; (Kodaira, JP) ;
Sakaihori; Minoru; (Kodaira, JP) ; Hiraki; Yuzo;
(Kodaira, JP) |
Correspondence
Address: |
MATTINGLY, STANGER, MALUR & BRUNDIDGE, P.C.
1800 DIAGONAL ROAD
SUITE 370
ALEXANDRIA
VA
22314
US
|
Family ID: |
34277631 |
Appl. No.: |
10/569627 |
Filed: |
August 25, 2004 |
PCT Filed: |
August 25, 2004 |
PCT NO: |
PCT/JP04/12176 |
371 Date: |
December 20, 2006 |
Current U.S.
Class: |
370/346 |
Current CPC
Class: |
H04W 4/029 20180201;
G08G 1/20 20130101; H04L 27/2078 20130101; H04W 4/02 20130101 |
Class at
Publication: |
370/346 |
International
Class: |
H04J 3/16 20060101
H04J003/16 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 27, 2003 |
JP |
2003-303256 |
Jan 6, 2004 |
JP |
2004-000806 |
Claims
1. A polling method in a digital radio communication system for
collecting information from a plurality of terminal stations by
polling, wherein a polling response signal to be transmitted from
each terminal station to a base station has a frame format
constructed of a one-frame in which a cyclic bit pattern is placed
at a leading end of the frame format.
2. The polling method in a digital radio communication system
according to claim 1, wherein a modulating system for signal
transfer is the .pi./4 shift QPSK system, and all bits in the
cyclic bit pattern are "0".
3. The polling method in a digital radio communication system
according to claim 1, wherein the modulating system for signal
transfer is the .pi./4 shift QPSK system, and each of all bits in
the cyclic bit pattern are a repetitive bit pattern comprising
binary values of "1"and "0".
4. A vehicle search method in a digital radio communication system
for collecting information from a plurality of terminal stations
into a base station by polling, wherein a polling response signal
to be transmitted from each terminal station to the base station
has a frame format constructed of a one-frame in which a cyclic bit
pattern is placed at a leading end of the frame format, and the
base station collects information from the terminal stations based
on the polling response signal constructed of the one-frame in
response to a request for allocation of a vehicle from a client.
Description
TECHNICAL FIELD
[0001] The present invention relates to a polling method and a
vehicle search method in a digital radio communication system, and
more specifically to a polling method and a vehicle search method
well adapted to a mobile communication system.
BACKGROUND ART
[0002] There has been known a digital radio communication system in
which, when digital information is transmitted via a radio
communication system, the information (such as a bit string of
binary signals) is divided into a prespecified number of bits to
generate a prespecified frame structure including the divided bit
string, and a received base band signal is modulated to a digital
signal by means of the modulation system such as the .pi./4 shift
QPSK (Quadrature Phase Shift Keying) system to transmit the digital
signal as a digitally modulated signal. The digital radio
communication system as described above is widely used as an AVM
(Automatic Vehicle Monitoring) system, for instance, for allocating
taxis with a radio communication system. In this case a particular
communication station functions as a master station (or a base
station), and a number of communication terminal stations (which
are sometimes referred to as in-vehicle stations or as slave
stations) makes communications under control by the master
station.
[0003] In the digital radio communication system as described
above, it is necessary for the master station to always recognize
information about a current state of each vehicle including a
position of a slave station in the car, whether a passenger is in
the vehicle or not, and whether any abnormality has occurred in the
vehicle or not, and the communication system referred to as
"polling system" is widely used. Refer to, for instance, Japanese
Patent Laid-Open Publication No. 5-284561 (patent document 1).
[0004] The digital radio communication system as described above is
described below with reference to FIG. 5. FIG. 5 schematically
shows a case in which the digital communication system as described
above is applied to a taxi radio communication system. For
instance, in-vehicle stations 502-1, 502-2, . . . 502-N are
connected to a master station 501. In the digital radio
communication system shown in FIG. 5, when the master station 501
tries to collect vehicle's current state information from each of N
units of in-vehicle stations, the master station 501 periodically
transmits a polling signal PO to the in-vehicle stations 502-1,
502-2, . . . 502-N to collect the vehicle's current state
information from each in-vehicle station as shown in FIG. 6. When
each of the n-vehicle stations 502-1, 502-2, . . . 502-N receives
the polling signal PO from the master station 501, the in-vehicle
stations 502-1, 502-2, . . . 502-N transmit polling response
signals S1, S2, . . . Sn including the vehicle's current state
information sequentially at a timing previously assigned to each
vehicle. The sequence of transmission of the polling response
signal after reception of a polling signal by each vehicle is
optional, and in the taxi radio communication system, the sequence
can be decided, for instance, according to vehicle's number of the
vehicles. There is no restriction over the method of deciding the
sequence.
[0005] For a communication system to be employed in the digital
radio communication system as described above, there are the
standard specifications based on a narrow band digital
communication system such as the digital SCPC (Single Channel Per
Carrier) system or the FDMA. In general, the communication system
is operated based on these standard specifications. In the standard
specifications, a frame format of a radio signal is based on the
Japanese standard ARIB STANDARD-T61 (referred to as ARIB STD-T61
below).
[0006] FIG. 2 and FIG. 3 illustrate signal frame formats based on
the ARIB STD-T61. FIG. 2 illustrates a frame format of a
synchronous burst SB. The synchronous burst SB is generally a
signal transmitted for establishing synchronicity in communications
when a communication channel is set and also when a channel is
switched. FIG. 3 illustrates a frame format of a communication
channel SC. Formats of the synchronous burst SB and the
communication channel SC constitute a frame as a minimum unit of a
radio communication signal, and radio communication is performed by
repeating the frame. The frame cycle is fixed to 40 ms.
[0007] In FIG. 2 and FIG. 3, a portion LP+R indicates a linearizer
preamble and bust transient response guard time, a portion P
indicates a preamble, a portion RICH indicates a radio information
channel, a portion SW indicates a synchronous word, a portion PICH
indicates a parameter information channel, a portion G indicates a
guard time, and a portion UD indicates a portion not defined yet.
Numerals in FIG. 2 and FIG. 3 indicate bit numbers respectively.
The abbreviates above are defined in the ARIB STD-T61 described
above.
[0008] FIG. 4 is a view illustrating an example of a frame
transmitted when communication is performed based on the SCPC
(Single Channel Per Carrier) system described above. As clearly
understood from this figure, to start communication, at first 1 to
3 frames of a synchronous burst SB are transmitted (although 2
frames are shown in FIG. 4), and then voice or non-voice
communication is performed via a communication channel SC. Then 2
frames of the communication channel SC comprising an aerial signal
are transmitted to notify termination of the communication.
[0009] The master station 501 and each of the in-vehicle stations
502-1 to 502-N perform signal transactions by means of the
demodulation system of, for instance, .pi./4 shift QPSK based on
the standard specifications. An example of a transmitter at each of
the in-vehicle stations 502-1 to 502-N is described below with
reference to a block diagram shown in FIG. 7. Also an example of a
receiver at the master station 501 is described with reference to a
block diagram shown in FIG. 8.
[0010] At first, the transmitter shown in FIG. 7 is described. Data
for ordinary voice communication or non-voice communication is
inputted to an outgoing data input terminal 701. In this step, also
data for vehicle's current state information transmitted from each
in-vehicle station for polling is inputted to this outgoing data
input terminal 701. The vehicle's current state information
includes data specific to each vehicle such as positional
information about an in-vehicle station (vehicle) on which the
transmitter is loaded and information as to whether a passenger is
in the vehicle or not.
[0011] Data for the vehicle's current state information inputted to
the outgoing data input terminal 701 is supplied to the channel
encoding section 702. The channel encoding section 702 adds
communication information required for communication to the
vehicle's current state information inputted to the outgoing data
input terminal 701 to generate a frame format for the synchronous
burst SB shown in FIG. 2 or for the communication channel SC shown
in FIG. 3. The channel encoding section 702 then supplies the frame
format as the 384-bit data to a S/P (serial/parallel) converting
section 703. The channel encoding section 702 operates under
control by a transmission control section comprising a
microcomputer or the like not shown, and is switched between a mode
for configuring a synchronous burst SB and a mode for configuring a
communication channel SC during operation.
[0012] When at first a synchronous burst SB is configured to
construct an outgoing frame shown in FIG. 4, the channel encoding
section 702 arrays data for LP+R, P, RICH, SW, P and G to form the
frame structure shown in FIG. 2 with 384-bit data constructed as a
whole, and supplies the resulting data as a synchronous burst SB to
the S/P (serial/parallel) converting section 703.
[0013] When an operating mode is switched to that for constructing
a communication channel SC to configure an outgoing frame, the
channel encoding section 702 performs encoding to correct errors
for the data inputted from the outgoing data input terminal 701 to
generate TCH data. The channel encoding section 702 then adds LP+R,
P, RICH, SW, and UD data to the TCH data to configure the frame
structure as shown in FIG. 3 for forming 384-bit data, and then
sends the 384-bit data as a communication channel SC to the S/P
(serial/parallel) converting section 703.
[0014] Then the S/P (serial/parallel) converting section 703
converts the data inputted from the channel encoding section 702 to
parallel data 2 bits by 2 bits with a symbol cycle T and supplies
the parallel data to the mapping section 704, where the symbol
cycle T is an inverse number of a symbol rate f.sub.b, and in the
ARIB STD-T61 standard, because the symbol rate f.sub.b is equal to
4.8 KHz, the symbol cycle T is 208 .mu.m. Two lines from the S/P
(serial/parallel) converting section 703 are connected to the
mapping section 704, and 1 bit are inputted through each of the
lines to the mapping section 704, namely 2 bits are inputted
simultaneously to the mapping section 704.
[0015] The mapping section 704 performs mapping in response to the
2-bit data inputted from the S/P (serial/parallel) converting
section 703 according to the known I-Q coordinate system. The
mapping is described later. As a result of mapping, the inphase
component is (I component) is imputed to an upsampler 705-1, while
the orthogonal component (Q component) is inputted to an upsampler
705-2. The upsamplers 705-1, 705-2 subjects the inphase component I
and the orthogonal component Q of a signal inputted from the
mapping section 704 to oversampling, namely, for instance, 16-times
oversampling (16 times of oversampling within a symbol cycle), and
inputs the resulting components to LPFs (low-pass filter) 706-1,
706-2.
[0016] The LPFs 706-1, 706-2 function to restrict a band of signals
inputted from the upsamplers 705-1, 705-2 to prevent interference
to an adjoining channel. The signals are then converted to analog
signals with D/A (digital/analog) converters 707-1, 707-2, and the
resulting analog signals are supplied to a transmission high
frequency section circuit and a power amplifier 708. The
transmission high frequency section circuit and the power amplifier
708 converts the base band signals outputted from the D/A
(digital/analog) converters 707-1, 707-2 to signals in a radio
frequency band and then supplies the signals, after power
amplification, from an outgoing signal output terminal 709 to an
antenna not shown in the figure for signal transmission.
[0017] FIG. 9 shows an example of configuration of the mapping
section 704, and output signals from the S/P converting section 703
(through the two lines described above) shown in FIG. 7 are
inputted via bit data input terminals 901-1, 901-2 to a table 902.
For the bit data b.sub.1 and b.sub.0 inputted from the input
terminals 901-1, 901-2 to the table 902, the bit data b.sub.1 is
inputted earlier as compared to the bit data b.sub.0 to the S/P
(serial/parallel) converting section 703 shown in FIG. 7 (b,
first).
[0018] The table 902 is configured with combinations of the input
bit data b.sub.1, b.sub.0 so that each of the values of 1, 3, -1,
and -3 can be obtained as an output d. Namely, 1 is obtained as the
output data d for the input bit data (b.sub.1, b.sub.0) of (0,0), 3
for (0,1), -1 for (1,0), and -3 for (1,1). The output d is inputted
to an accumulator 903.
[0019] The accumulator 903 has an internal memory (a memory in
which the content is reset to 0 when power is turned ON). The
accumulator 903 adds the content therein to a value d inputted from
the table 902, stores a result of addition s again in the memory,
and also input the result of addition s to a surplus computing
circuit 904. The surplus computing circuit 904 computes a surplus m
(=s mod 8) obtained by dividing the output value s from the
accumulator 903 by 8, and inputs the surplus m into the table
905.
[0020] The table 905 outputs 8 types of mapping value according to
a value m inputted from the surplus computing circuit 904, and the
inphase component I is inputted to the upsampler 705-1 shown in
FIG. 7 via the inphase component output terminal 906-1, while the
orthogonal component Q is inputted to the upsampler 705-2 via the
orthogonal component output terminal 906-2. Therefore, the inphase
component I and orthogonal component Q, which are output values
from the table 905, can be developed on an I-Q coordinate plane as
shown in FIG. 10.
[0021] A receiver at the base station 501 shown in FIG. 8 is
described below. An antenna not shown is connected to an incoming
signal input terminal 801. A signal transmitted from the
transmitter shown in FIG. 7 is received by the antenna, and the
incoming signal is inputted to an incoming high frequency wave
section circuit 802. The incoming high frequency wave section
circuit 802 converts the incoming signal in the radio frequency
band to a signal in an intermediate frequency band to supply the
same to an A/D converter 803 for digitizing the signal. Then, the
digitized signal is supplied to an orthogonal demodulating section
804.
[0022] A signal for the inphase component I and a signal for the
orthogonal component Q, both of which are transmitted from the
receiver, are outputted from the orthogonal demodulating section
804 and are supplied to the LPFs 805-1 and 805-2 respectively. In
the LPF 805-1, unnecessary frequency components are removed from
the signal for inphase component I, and in the LPF 805-2,
unnecessary frequency components are removed from the signal for
orthogonal component Q.
[0023] The output signals from the LPFs 805-1, 805-2 are supplied
to downsamplers 806-1, 806-2 respectively, where only data for one
symbol cycle is taken out in the downsamplers and inputted to a
demodulating section 807. Timing for taking out the unnecessary
frequency components in the downsamplers 806-1, 806-2 is controlled
by a timing synchronizing section not shown so that the unnecessary
frequency components are correctly taken out according to the
symbol timing (in synchronism to a symbol).
[0024] In the demodulating section 807, symbol determination is
performed according to the inphase component I and orthogonal
component Q inputted from the downsamplers 806-1, 806-2, and 2-bit
determination data is supplied to a P/S (Parallel/serial)
converting section 808 to convert the 2-bit data to serial data,
which is inputted to a channel decoding section 809. The channel
decoding section 809 separates necessary information and data from
the data inputted from the P/S converting section 808, namely
decodes a frame structure of a communication channel SC shown in
FIG. 3, extracts data from TCH section, decodes the data to obtain
incoming data, and outputs the data from an output terminal 810 to
supply the data to a data processing section not shown.
[0025] It should be noted that FIG. 8 shows a case in which the
incoming high frequency wave section circuit 802 operates according
to the super heterodyne system. When the incoming high frequency
wave section circuit 802 operates according to the direct
conversion system, the inphase component I signal and the
orthogonal component Q signal are outputted directly from the
incoming high frequency wave section circuit 802. In this case, the
inphase component I signal and the orthogonal component Q signal
outputted from the incoming high frequency wave section circuit 802
are inputted separately via the A/D converter into the LPFs 805-1,
805-2 respectively. Therefore, the orthogonal demodulating section
804 is not necessary.
[0026] In the prior art, the system shown in FIG. 4 is applied also
to a polling response signal sent from an in-vehicle station to a
base station, after a synchronous burst SB is transmitted by 1 to 3
frames, voice communication or non-voice communication is performed
via the communication channel SC, and then a communication channel
SC comprising an aerial line signal is transmitted by 2 frames to
notify an end of communication.
[0027] Radio communication between the base station and in-vehicle
stations 502-1 to 502-N have been described above. In a radio
communication system such as an AVM system for allocating taxies
based on the prior art, a current position of an in-vehicle station
as a mobile station (a vehicle such as a taxi) is detected with the
GPS (Global Positioning System) by and stored in the in-vehicle
station itself. Each mobile station returns vehicle's current
position information as a response by using a response slot
dedicated to each mobile station according to a polling signal
cyclically sent from the base station. The base station
sequentially performs polling to all vehicles which are mobile
stations to grasp current position information about all of the
mobile stations. In the system as described above, there is at
least one base station which is connected to a management center,
and the management center searches an optimal vehicle from the
current position information sent from the mobile stations
according to a request for allocation of a vehicle from a client
and allocates the vehicle (taxi).
DISCLOSURE OF THE INVENTION
[0028] In the prior art, there is no countermeasures against the
problem that the time required for polling increases in association
with increase of slave terminals, and because of this problem,
efficient communication can not be realized.
[0029] Furthermore in the prior art, also when a polling response
signal is transmitted from a in-vehicle station to the base
station, at first a synchronous burst SB is transmitted by 1 to 3
frames, and then voice communication or non-voice communication is
performed through the communication channel SC, and then an end of
the communication is notified by sending the communication channel
SC comprising an aerial signal by 2 frames. In this case, even when
a data volume required for transmission of vehicle's current state
information to be transmitted in response to polling is satisfied
with one frame of the communication channel SC, it is necessary to
send data comprising at least 4 frames (=160 ms), namely 1 frame
for the synchronous burst, 1 frame for the communication channel,
and 2 frames for the aerial signal, and for instance. When it is
necessary to collect vehicle information from 400 taxies, at least
a time period of 64 seconds is required for collecting information
from all of the vehicles by performing polling once.
[0030] It is conceivable to burst only 1 frame for the
communication channel SC shown in FIG. 3 as a polling response
signal from each in-vehicle station to shorten the time required
for collecting information by polling. In this method, the time
required for collecting information from all vehicles can be
shortened, but there is the problem that ACG (Automatic Gain
Control) in a receiver at the base station can not be stabilized at
a leading end of a frame.
[0031] Moreover, when AFC (Automatic Frequency Control) is applied
to a receiver at the base station, an error is generated also in an
operation for AFC due to an error in symbol timing synchronization,
and accordingly the error rate in TCH data increases. Especially,
in the taxi radio communication system in which slave stations move
around, a distance between the base station and each in-vehicle
station and a situation of propagation of electric waves inevitably
change. Accordingly, a received power of a signal from each
in-vehicle station changes at the base station. Therefore, when the
base station receives a signal from each in-vehicle station, it is
necessary that the AGC sufficiently function for each frame, but in
the method described above, it is not possible to stabilize AGC at
a leading end of each frame. As a result, the AGC can not be
stabilized before a leading end of the TCH data inserted in a
forward section of each frame, which leads to increase of the error
rate.
[0032] The AFC in a general receiver is performed by using a known
preamble pattern included in a synchronous burst. Therefore, when a
burst comprising only 1 frame is transmitted as an outgoing frame,
for providing AFC to a signal from the base signal to each
in-vehicle station, there is no way but to use a synchronous word
SW which is a known pattern signal. However, when a synchronous
word SW is used as described above, to provide AFC, it is necessary
to establish synchronicity in the symbol timing. When there is an
error in the symbol timing synchronicity, an error is generated in
an operation for AFC, so that the receiving error rate increases in
TCH data.
[0033] Therefore, in the prior art as described above, it is
necessary to transmit data with the length of at least 4 frames
(=160 ms) as a polling response signal transmitted from an
in-vehicle station to the base station. Therefore, as described
above, the problem occurs that at least a time period of at least
64 seconds is required for colleting information from all of 400
taxies by polling once. The system as described above can not be
applied to a large scale taxi allocating system, and the number of
in-vehicle stations to be connected to the base station is at most
about 100.
[0034] It is an object of the present invention to provide a
polling system based on a digital radio communication system
enabling efficient communication.
[0035] It is another object of the present invention to provide a
polling method based on a digital radio communication system
enabling reduction of time required for polling without
causing-increase in an error rate.
[0036] It is still another object of the present invention to
provide a vehicle searching method enabling collection of vehicle's
current state information from in-vehicle stations within a short
period of time and efficient allocation of vehicles even in a large
scale system.
[0037] The present invention provides a polling method in a digital
radio communication system for collecting information from a
plurality of terminal stations by polling, wherein a polling
response signal to be transmitted from each terminal station to a
base station has a frame format constructed of a one-frame in which
a cyclic bit pattern is placed at a leading end of the frame
format
[0038] Furthermore the polling method in a digital radio
communication system according to the present invention is
configured such that a modulating system for signal transfer is the
.pi./4 shift QPSK system, and all bits in the cyclic bit pattern
are "0".
[0039] The polling method in a digital radio communication system
according to the present invention is configured such that the
modulating system for signal transfer is the .pi./4 shift QPSK
system, and each of all bits in the cyclic bit pattern are a
repetitive bit pattern comprising binary values of "1" and "0".
[0040] The present invention provides a vehicle search method in a
digital radio communication system for collecting information from
a plurality of terminal stations into a base station by polling,
wherein a polling response signal to be transmitted from each
terminal station to the base station has a frame format constructed
of a one-frame in which a cyclic bit pattern is placed at a leading
end of the frame format, and the base station collects information
from the terminal stations based on the polling response signal
constructed of the one-frame in response to a request for
allocation of a vehicle from a client.
[0041] The present invention provides a digital radio communication
system in which a base station collects information from each of a
plurality of terminal stations by polling, wherein the terminal
station comprises a data input section, a channel encoding section
for adding information required for communication to the input data
to configure a frame of the polling response signal, a mapping
section for mapping output from the channel encoding section, and a
high frequency wave section for subjecting the mapped data formed
in the mapping section to high frequency conversion for
amplification, and wherein a polling response signal generated in
the channel encoding section has a frame format constructed of a
one-frame in which a cyclic bit pattern is placed at a leading end
of the frame format.
[0042] The present invention provides a vehicle searching method in
a digital radio communication system in which a base station
collects information from each of a plurality of terminal stations
by polling, and the terminal station comprises a data input
section, a channel encoding section for adding information required
for communication to the input data to configure a frame of the
polling response signal, a mapping section for mapping output from
the channel encoding section, and a high frequency wave section for
subjecting the mapped data formed in the mapping section to high
frequency conversion for amplification, wherein a polling response
signal generated in the channel encoding section has a frame format
constructed of a one-frame in which a cyclic bit pattern is placed
at a leading end of the frame format, and wherein in response to a
request for allocation of a vehicle from a client, the base station
collects information from the terminal stations based on the
polling response signal constructed of the one-frame.
[0043] With the present invention, it is needless to say that-the
time required for collecting information by polling can be
shortened, and also AGC and AFC for a receiver can be provided in
the stable state. Furthermore, an operation for polling to all
vehicles can be performed at a high speed, and therefore, even in a
system comprising several hundreds of mobile stations, the base
station can search a mobile station at an optimal location, and
also can search vehicles correctly.
BEST MODE FOR CARRYING OUT THE INVENTION
[0044] The polling method in a digital radio communication system
according to the present invention is described in detail below
with reference to an embodiment thereof shown in the figures. Also
in the embodiment of the present invention described below, a
transmitter at each in-vehicle station (mobile station) has the
same block configuration as that of the receiver shown in FIG. 7.
Also a receiver at the base station has the same block
configuration as that of the receiver shown in FIG. 8.
[0045] However, a polling response signal transmitted from the
transmitter shown in FIG. 7 is different in format from that in the
prior art. As a result, also processing for receiving a polling
response signal by the receiver in FIG. 8 is different from that in
the prior art. Therefore, a weight is put on the differences in the
following description.
[0046] At first, FIG. 1 illustrates a frame format of a polling
response burst SP sent as a polling response signal from the
transmitter shown in FIG. 7. In this embodiment, the polling
response burst SP is sent by only one frame to polling from the
base station.
[0047] In this embodiment, the channel encoding section 702 in the
transmitter at the in-vehicle station shown in FIG. 7 configures a
polling response signal by selecting, in addition to a frame format
of the synchronous burst SB shown in FIG. 2 and a frame format of
the communication channel SC shown in FIG. 3, also a format of the
polling response burst SP shown in FIG. 1 according to the
necessity and sends the polling response signal to the S/P
(serial/parallel) converting section 703.
[0048] The frame format of the polling response burst SP shown in
FIG. 1 is described below. In FIG. 1, a 44-bit linearizer preamble
and a burst transient response guard time LP+R are located at a
leading end. Subsequently, a 20-bit synchronous word SW, a 56-bit
radio information channel RICH, and a 256-bit traffic channel TCH
are placed successively, and an 8-bit guard time G is placed at a
trailing end to provide 384-bit data in all.
[0049] The reason why the frame format as described above is
employed is described below by comparing a frame format of the
synchronous burst SB shown in FIG. 2 to a frame format of the
communication channel SC shown in FIG. 3. At first, the synchronous
word SW and the radio information channel RICH are described. In
this polling response burst SP, the synchronous word SW is
forwardly moved from a central portion of the frame, so that a work
load to the receiver for synchronicity processing can be
reduced.
[0050] The radio information channel RICH includes information
required in the receiving side to recognize that a signal
transmitted from a transmitter at an in-vehicle station and
received by a receiver at the base station is a non-voice polling
response signal. Because of this configuration, the receiver at the
base station can easily determine whether the received signal is a
non-voice polling response signal or not.
[0051] On the other hand, the linearizer preamble and burst
transient response guard time LP+R are used for training a
transmitter linearizer, and their signal contents are not specified
in the communication channel SC shown in FIG. 3.
[0052] In the polling response burst SP shown in FIG. 1, a signal
pattern of the linearizer preamble LP for the linearizer preamble
and burst transient response guard time LP+R is configured with
only "0" for all bits or with repetition of binary values "1" and
"0". With he configuration as described above, the linearizer
preamble and burst transient response guard time LP+R can be used
not only form training the transmitter linearizer, but also for
providing AGC and AFC to the receiver.
[0053] At first a case is described in which the linearizer
preamble LP is configured only with a "0" bit pattern for all bits.
In this case, to form a polling response burst SP, in the mapping
section 704 of the transmitter shown in FIG. 7, all of the bit data
b.sub.1, b.sub.0 inputted from the input terminals 901-1, 901-2 in
FIG, 9 are set to "0", namely (b.sub.1, b.sub.0) is always (0,0).
Therefore, the bit data d outputted to the accumulator 903 from the
table 902 shown in FIG. 9 is always set to 1 (d=1).
[0054] As a result, because an output s from the accumulator 903
increments by 1 like 0, 1, 2, . . . for each symbol, an output from
the surplus computing circuit 904 changes from 0 to 7 following the
repetition of 0, 1, 2, . . . with 8 symbol cycles. Output values
from the mapping section 704 correspond to the mapping points
angularly displaced by .pi./4 radians along a unit circle on the
I-Q coordinate plane shown in FIG. 10.
[0055] The output values are upsampled by the upsamplers 705-1,
705-2. Base band signals filtered by the LPFs 706-1, 706-2, and
then outputted from the D/A converters 707-1, 707-2 go around
counterclockwise on the unit circle once for every 8 symbols.
[0056] Next a case is described in which the linearizer preamble LP
portion is configured with the repetitive bit patterns of binary
values "1" and "0". In the mapping section shown in FIG. 9, the bit
data b.sub.1 is "1" and bit data b.sub.0 is "0". Namely (b.sub.1,
b.sub.0) is always (1,0).
[0057] Therefore, always a value d of -1 is always inputted from
the table 902 to the accumulator-903. As a result, an output from
the surplus-computing circuit 904 changes in a direction opposite
to that described above like 0, 7, 6, . . . , 0, 7, 6, . . . , and
therefore the base band signals outputted from the D/A converters
707-1, 707-2 go around along the unit circle once for every 8
symbols clockwise on the I-Q coordinate plane shown in FIG. 10.
[0058] When the polling response burst SP is transmitted and
received by the receiver shown in FIG. 8, also the received base
band signals outputted from the LPFs 805-1, 805-2 goes around with
the same cycle.
[0059] With the bit patterns as described above, output signals
from the LPFs 805-1, 805-2 are base band signals with an 8-symbol
cycle, and thereby a frequency deviation .DELTA.f can easily be
detected from this signal.
[0060] The frequency deviation .DELTA.f can easily be detected from
the base band signals each with an 8-symbol cycle which are output
signals from the LPFs 805-1, 805-2 by using the method described in
the specification for Japanese Patent Application No. 2003-167966
filed by the inventor of the present invention. Detailed
description of the method is omitted, and only brief description is
provided herein.
[0061] At first, base band signals which are preamble signals
comprising a repetitive pattern of N.sub.ptn symbols, namely base
band signals each with an 8-symbol cycle which are output signals
from the LPFs 805-1, 805-2 are oversampled N.sub.ov times per
symbol (N.sub.ov: positive integer of 2 or more). Then an optional
number of successive N.sub.win sample base band signals (N.sub.win:
positive integer of 2 or more) are extracted, and of the self
function r(m)=Sx(n)x*(n-m) for the extracted N.sub.win sample base
band signals x(n) (n=0, 1, . . . N.sub.win -1) (wherein S indicates
a sum of n=m, m+1, . . . N.sub.win-1; m indicates a non-negative
integer, and * in x*(n-m) indicates a complex conjugate),
r(N.sub.ptn N.sub.ov) (N.sub.ptn: 8) is computed to obtain a phase
.theta. of the r(N.sub.ptn N.sub.ov).
[0062] By using the phase .theta. and setting the symbol rate to
fb, the frequency deviation .DELTA.f is computed as .theta.
fb/2N.sub.ptn .pi.. When the frequency deviation .DELTA.f is
computed as described above, AFC can easily be provided to a
receiver by using the frequency deviation .DELTA.f.
[0063] In this embodiment, when the receiver shown in FIG. 8
receives the polling response burst SP shown in FIG. 1, the
receiver recognizes the fact according to information set in the
radio information channel RICH, and detects the frequency deviation
.DELTA.f by executing the processing procedure described above.
Then AFC is provided to the receiver by using this frequency
deviation .DELTA.f. As described in the specification referred to
above, because the frequency deviation .DELTA.f can be detected
regardless of synchronicity of a symbol timing, the AFC operation
does not give any influence over the synchronicity of symbol
timing. Therefore AFC can always be provided in the stable state in
this embodiment, and increase of the error rate never occurs.
[0064] For AGC to a receiver, an average of signal powers outputted
from the LPFs 805-1, 805-2 shown in FIG. 8, an average of RSSI
(Received Signal Strength Indicator) signals outputted from the
incoming high frequency wave section circuit 802, or an average of
the two types of averages described above is used.
[0065] In this case, a gain by the incoming high frequency wave
section circuit 802 is controlled according to the average power
described above to maintain amplitude of signals inputted to the
A/D converter 803. However, if the prior art is used in this step,
control in a forward portion of a frame is not stabilized yet as
described above.
[0066] On the other hand, with the frame format shown in FIG. 1, a
linearizer preamble LP is placed at a leading end of a frame, and
this portion is configured with the all bit "0" pattern or a
repetitive pattern of binary values "1" and "0". Because bits in
this portion do not provide any information, AGC can easily be
stabilized before the synchronous word SW portion, and increase of
an error rate never occurs.
[0067] In a case of the bit pattern of the polling response burst
SP, namely when the polling response burst SP is configured with
the bit pattern of all bit "0" pattern or with a repetitive pattern
of binary values of "1" and "0", the burst signals go around in the
base band on the I-Q coordinate plane, so that the envelope curve
becomes constant. As a result, also powers of the RSSI signal and
outputs from the LPFs 805-1, 805-5 are kept at constant values.
Because of the feature as described above, in this embodiment, AGC
can easily be stabilized before the synchronous word SW, and also
an average power required for the operation can be computed by
averaging within a short period of time. Therefore, with this
embodiment, AGC control can be obtained with a simple
configuration.
[0068] As described above, when the frame format shown in FIG. 1 is
employed for the polling response burst SP, a receiver at the base
station can provide sable AGC and AFC operations only by receiving
the one-frame polling response burst SP. As a result, the time
required for collection of vehicle's current state information by
polling can be shortened as compared to that in the prior art. When
vehicle's current state information is to be collected from 400
taxies, the time required for collecting the information is 64
seconds in the prior art, but only 16 seconds suffice in this
embodiment. In the embodiment of the present invention, the time
required for polling can be shortened without causing increase in
the receiving error rate, which enables efficient operations for
polling.
[0069] An optimal vehicle searching method using the high speed
polling method described above is described below. At first,
problems in the conventional vehicle searching method are described
below for facilitating the understanding of the present invention.
FIG. 11 illustrates a system of polling all mobile stations
(taxies) in an AVM system for allocation of taxies based on the
prior art. FIG. 11(a) shows a polling signal PO sent from the base
station 501. In this case, a polling signal PO comprises, for
instance, 5 frames (1 frame=40 ms), and length of one polling
system is 200 ms. In this case, the data collection speed is 2,400
bps. When the polling signal is sent to 300 mobile stations, the
polling cycle T including a pause period is about 60.4 seconds.
[0070] In response to the polling signal PO, all of the in-vehicle
stations 502-1, 502-2, . . . 502-N transmit polling response
signals S1, S2, . . . Sn respectively at a prespecified timing to
the base station 501 as shown in FIG. 11(b). Therefore, in this
polling system, the polling cycle T1 is 60.4 seconds, and about one
minute is required for recognizing positions of all vehicles.
Namely search for vehicles can be performed only once within a
one-minute cycle.
[0071] FIG. 14(a) indicates contents of a polling signal PO, while
FIG. 14(b) indicates a polling response signal S. In FIG. 14(a),
data length (polling signal length) is 200 ms, and a signal type
1401 is information indicating that the signal is a polling signal.
A polling vehicle number specification 1402 is information used for
collecting current state information of each in-vehicle station,
for instance, by specifying any of the in-vehicle stations 502-1,
502-2, . . . 502-N. A reference numeral 1403 denotes a spare bit.
Also in FIG. 14(b), also the data length (polling response signal
length) is 200 ms, and a signal type 1404 is information indicating
that the signal is a polling response signal. Current state
information 1405 is vehicle's current state information such as
information as to whether a vehicle in which a corresponding
in-vehicle station is loaded is occupied by a passenger or not, a
vehicle speed, or any abnormal state in the vehicle. Positional
information 1406 indicates a current position of a vehicle which an
in-vehicle station in the vehicle acquires from the GPS, and the
information is expressed, for instance, by longitude and
latitude.
[0072] Thus, because a polling cycle for searching vehicles is
performed once in each polling cycle in this type of AVM system for
allocation of taxies based on the prior art, the positional
information can be acquired once in one minute. Therefore, when
allocation of a vehicle is requested from a client, the management
center allocates a vehicle based on positional information one
minute earlier, resulting in that optimal allocation of an optimal
vehicle can not be carried out. This problem becomes more serious
as an AVM system for taxi allocation becomes larger.
[0073] FIG. 12 is a general block diagram illustrating an
embodiment of an optimal vehicle searching method according to the
present invention, and this figure illustrates an example of the
AVM system for taxi allocation making use of GPS. Referring to FIG.
12, the reference numerals 1201-1, 1201-2, . . . 1201-n denote base
stations. The base stations are generically referred to as a base
station 1201. Reference numeral 1202 indicates a management center,
which is connected to a plurality of base stations 1201 via a
dedicated line 1203. Reference numerals 1204-1, 1204-2, . . . ,
1204-N denote mobile stations (in-vehicle stations) respectively.
The mobile stations are generically referred to as a mobile station
1204. Reference numeral 1205 denote a communication area, namely a
communication zone in which the base station 1201-1 can communicate
with the mobile stations 1204, and the mobile station 1204-1 within
this communication area 1205 can communicate with the base station
1201-1. Reference numeral 1206 indicates a GPS satellite, and each
mobile station 1204 can acquire positional information (by latitude
and longitude) of own vehicle by receiving positional information
1207 from the GPS satellite 1206. In response to an instruction
from the management center 1202, each base station 1201 transmits a
polling signal PO to each of the mobile stations 1204, and the
mobile stations send polling response signals S1, S2, . . . , Sn to
the respective base stations in response to the polling signal PO.
In other words, this system is such that the management center 1202
collects vehicle's current state information from the mobile
stations 1204 in the communication area 1205 according to a
sequence of vehicle numbers according to a specification of a
vehicle number for each mobile station from each base station 1201.
In the present invention, radio communication between the base
station and the mobile stations is performed based on, for
instance, the digital SCPC system. It is to be noted that the
management center 1202 may be integrated with the base station
1201.
[0074] Next, the polling system used in the optimal vehicle search
method according to the present invention is described below with
reference to FIG. 13 and FIG. 15. FIG. 13(a) illustrates a polling
signal PO1 transmitted from the base station 1201 in FIG. 3. This
polling signal PO1 has the signal length of 40 ms. This signal has,
for instance, the format of the communication channel SC shown in
FIG. 3, and therefore in the polling signal PO1, 96 bits for the
radio information channel RICH, a synchronous word SW, and an
undefined section UD are configured into 1 frame (40 ms), and all
of other bits are set to "0". Because the polling signal PO1 has
the signal length of 40 ms, for instance, when polling is performed
to all of 300 mobile stations, the polling cycle T2 is 12.4 seconds
including the pausing time. In other words, vehicle search can be
made once for every 12.4 seconds. FIG. 13(a) illustrates only the
polling signal PO1, but typically the base station always transmits
an aerial signal to establish synchronicity between the base
station and each mobile station.
[0075] FIG. 15(a) illustrates contents of the polling signal PO1.
The polling signal PO1 is configured of a signal type 1501, a
polling vehicle specification 1502, and a spare 1503, and the data
length (polling signal length) is 40 ms.
[0076] In response to this polling signal PO1, the mobile stations
1204-1, 1204-2, . . . , 1204-N send polling response signals SR1,
SR2, . . . , SRn at a prespecified timing from each in-vehicle
station to the base station 1201 respectively. The polling response
signals are generically referred to as a polling response signal
SR. Therefore in this polling system according to the present
invention, a polling cycle T2 for 300 mobile stations is a
repetition of 12.4 seconds, and a position of each of the 300
vehicles can be recognized once for every 12.4 seconds for
searching each vehicle.
[0077] FIG. 15(b) illustrates contents of the polling response
signal SR. The polling response signal SR is configured of a signal
type 1504, current state information 1505, and positional
information 1506, and the data length (polling response signal
length) is 40 ms. Contents of each data shown in FIG. 15 is the
same as those shown in FIG. 14.
[0078] The 1 frame (96 bits, 40 ms) is used as a polling signal PO1
from the base station 1201, while the polling signal PO, an aerial
signal, data and the like are also transmitted from the base
station, and all of the signals and data include a synchronous word
SW. Therefore, each mobile station can perform the processing for
establishing synchronicity with the base station according to the
synchronous word.
[0079] The polling response signal SR from the mobile station 1204
is transmitted from each mobile station according to a different
timing and at a different transmission level, and generally several
frames are transmitted to start communications as shown in FIG. 4.
In this method, however, the polling speed can not be raised, and
therefore in the polling system according to the present invention,
one frame (96 bits, 40 ms) is used also for the polling response
signal SR like for the polling signal PO1. The polling response
signal SR may be one frame for the reason described with reference
to FIG. 1 illustrating the embodiment of the present invention
described above. Namely, in FIG. 1, a polling response burst SP
transmitted as a polling response signal is transmitted by only one
frame. Because a leading end of this frame is configured as a
all-bit "0" pattern, or a repetitive pattern of binary values "1"
and "0", AGC for a receiver in the base station 1201 can be
provided in the stable station. Because no error occurs in the AGC
operation, increase in an error rate never occurs. Therefore, even
though the polling response signal SR is configured of only one
frame, the base station 1201 can accurately collect vehicle's
current station information from each mobile station 1204. In this
context, the polling response signal SR is described as a 96-bit
signal, but in FIG. 1, the polling response signal is illustrated
as a 384-bit signal, because the figures shows the state after
coding defined in ARIB STD-T61, namely CRC coding, insertion of
fixed bits, convolution coding, and interleave are performed.
[0080] The polling signal PO1 shown in FIG. 13(a) has the signal
length of 40 ms, and is used for polling with the cycle T2 of 12.4
seconds. On the other hand, the mobile station sends a polling
response signal with the signal length of 40 ms to the base station
1201 as shown in FIG. 13(b). When there are 300 mobile stations,
the base station 1201 sends polling signals PO1 to all of the
mobile stations within the communication area 1205 specifying each
of the mobile station vehicle numbers 1 to 300. Each mobile station
1204 computes the timing for sending a polling response signal
based on a vehicle number previously assigned to the mobile
station, and sends a polling response signal SR in the
corresponding transmission slot. Furthermore, the base station 1201
sends a polling signal, after passage of the pausing time,
specifying each mobile station vehicle numbers starting from 1 up
to 300, and thus the base station can collect current state
information from all of the mobile stations in the communication
area 1205 by repeating the same operation. In the present
invention, the digital SCPS system is used as a radio communication
system for business service, and therefore the data transfer rate
is 9,600 bps. Thus the time required for collecting positional
information from all of the mobile stations is 12.4 seconds.
[0081] Next the optimal vehicle search method using the polling
system according to the present invention is described with
reference to FIG. 16. FIG. 16(a) provides a map screen 1603
displaying a client 1601 requesting allocation of a vehicle and a
road 1602. This map screen 1603 is displayed, for instance, on a
display unit of a personal computer (not shown) at the management
center 1202. A case in which the client 1601 hoping allocation of a
vehicle sends a request for allocation of a vehicle to the
management center 1202 at a time point t1 is described with
reference to FIG. 16(b) and FIG. 16(c).
[0082] At first, the vehicle search method using the conventional
polling system shown in FIG. 11 is described. It is assumed in the
following description that the management center 1202 accepts a
request for allocation of a vehicle from the client 1601 at the
time point t1. Because the polling cycle T1 of the polling signal
shown in FIG. 11 is 60.4 seconds, so that the management center
1202 issues, at the time point t1, an instruction for allocation to
a vehicle not occupied by a passenger at a position closest to the
client 1601 based on positional information collected from the
mobile stations 1204 1 minute earlier by performing polling.
Namely, in FIG. 16(b), assuming that polling information is
collected from mobile stations 1604 and 1605 1 minute earlier by
polling, the mobile station 1605 is closer to the client 1601 at
this time. Therefore the management center issues an instruction
for allocation of a vehicle to the mobile station 1065.
[0083] In contrast, the vehicle search method using the polling
system according to the present invention as shown in FIG. 13 is
described below. It is assumed in the following description that
the management center 1202 accepts a request for allocation of a
vehicle from the client 1601 also at the time point t1. Because the
polling cycle T2 of the polling signal shown in FIG. 13 is 12.4
seconds, the management center 1202 issues an instruction for
allocation of a vehicle to a mobile station of a vehicle not
occupied with a passenger and closer to the client 1601 based on
the positional information of the mobile stations 1204 collected
12.4 second earlier by polling. Namely, as shown in FIG, 16(c),
because the mobile stations 1604 and 1605 are moving on the road
1602, unlike the positions of the mobile stations recognized by
polling 12.4 seconds earlier, actually the mobile station 1604 is
closer to the client 1601. Therefore the management center issues
an instruction for allocation of a vehicle to the mobile station
1604. In other words, actually a moving velocity of each mobile
station is faster, and the mobile stations 1604 becomes more closer
to a position of the client. Therefore, with the polling system
according to the present invention performed with the polling cycle
of 12.4 seconds, it is possible to collect positional information
of each mobile station at the oldest about 12 seconds earlier, so
that the mobile station 1604 can accurately be recognized as an
optimal vehicle for allocation. As described above, when the time
required for collecting, for instance, positional information of
mobile stations by polling is shortened, an instruction for
allocation of a vehicle can be issued to a mobile station closest
to a position of a client hoping allocation of a vehicle. Thus an
optimal vehicle allocation system can be constructed, which enables
efficient administration of a taxi radio allocation system.
[0084] The present invention has been described in detail above,
but the present invention is not limited to the examples of the
polling method and optimal vehicle search method based on a digital
radio communication system described above, and the present
invention can widely be applied to a polling method and an optimal
vehicle search method based on other types of digital radio
communication systems.
BRIEF DESCRIPTION OF THE DRAWINGS
[0085] FIG. 1 is an explanatory view illustrating an example of a
polling response signal employed in an embodiment of a polling
method in a digital radio communication system according to the
present invention;
[0086] FIG. 2 is an explanatory view illustrating an example of a
frame structure of an synchronous burst;
[0087] FIG. 3 is an explanatory view illustrating an example of a
frame configuration of a communication channel;
[0088] FIG. 4 is an explanatory view showing an example of a frame
transmitted when communication is performed based on the SCPC
system;
[0089] FIG. 5 is a block diagram showing an example of a digital
radio communication system used for collecting information from
each terminal station by polling;
[0090] FIG. 6 is an explanatory view showing a timing relation
between a polling signal and a polling response signal when
information is collected by polling;
[0091] FIG. 7 is a block diagram showing an example of a
transmitter at an in-vehicle station;
[0092] FIG. 8 is a block diagram showing an example of a receiver
at a base station;
[0093] FIG. 9 is a block diagram showing an example of a mapping
section of a transmitter;
[0094] FIG. 10 is an explanatory view illustrating an output value
from a table in the mapping section in an application of the
present invention shown on the I-Q coordinate plane;
[0095] FIG. 11 is an explanatory view showing a timing relation
between a polling signal and a polling response signal when
information is collected based on a polling system based on the
prior art;
[0096] FIG. 12 is a block diagram showing an example of a digital
radio communication system using the polling system according to
the present invention;
[0097] FIG. 13 is an explanatory view showing a timing relation
between a polling signal and a polling response signal when
information is collected based on the polling system according to
the present invention;
[0098] FIG. 14 is a view illustrating contents of a polling signal
and a polling response signal based on the prior art;
[0099] FIG. 15 is a view illustrating contents of a polling signal
and a polling response signal according to the present invention;
and
[0100] FIG. 16 is a view showing a display screen for illustrating
an example of an optimal vehicle search system according to the
present invention.
DESCRIPTION OF SYMBOLS
[0101] 501: Base station, [0102] 502-1 to 502N: In-vehicle station
[0103] 701: Transmitted data input terminal [0104] 702: Channel
encoding section [0105] 703: S/P (serial/parallel) converting
section [0106] 704: Mapping section [0107] 705-1, 705-2: Upsampler
[0108] 706-1, 706-2, 805-1, 805-2: LPF (low-pass filter) [0109]
707-1, 707-2: D/A digital/analog) converter [0110] 708: High
frequency wave section circuit and power amplifier [0111] 709:
Outgoing signal output terminal [0112] 801: Incoming signal input
terminal [0113] 802: Incoming high frequency wave section circuit
[0114] 803: A/D (analog/digital) converter [0115] 804: Orthogonal
component demodulating section [0116] 806-1, 806-2: Downsampler
[0117] 807: Demodulating section [0118] 808: P/S (parallel/serial)
converting section [0119] 809: Channel decoding section [0120] 810:
Received data output terminal [0121] 901-1, 901-2: Bit data input
terminal [0122] 902, 905: Table [0123] 903: Accumulator [0124] 904:
Surplus computing circuit [0125] 906-1: Inphase component output
terminal [0126] 906-2: Orthogonal component output terminal [0127]
1201-1 to 1201-n: Base station [0128] 1202: Management center
[0129] 1203: Communication-dedicated line [0130] 1204-1 to 1204-N:
Mobile station [0131] 1205: Communication area [0132] 1206: GPS
satellite [0133] 1207: Positional information [0134] 1601: Client
[0135] 1602: Road [0136] 1603: Display screen [0137] 1604, 1605:
Mobile station
* * * * *