System for detecting position of object having data carrier

A plurality of data carriers are prepared and possessed by, for example, persons who enter a building. The data carrier spread spectrum modulates a carrier signal of a predetermined frequency by an assigned Gold series corresponding to an ID code and transmits the modulated signal. Leaky cables each having a predetermined length are two-dimensionally distributed and arranged in the building. A frequency converter is connected to one end of each of the leaky cables and frequency converts the spread spectrum signal from the data carrier which has propagated the leaky cable into a frequency unique to the cable and sends the converted frequency signal to a central receiving unit through a transmission cable. The receiving unit individually demodulates the signal series from the reception signals and sequentially executes correlation calculations between the signal series and the Gold series assigned to the data carriers. The position of the leaky cable where the data carrier exists is obtained on the basis of a time difference between the time when a correlation peak value of the reception signal series demodulated by the frequency unique to the data carrier has been obtained by the correlation calculations and the time when a correlation peak value of the reception signal series demodulated by the frequency unique to the leaky cable has been obtained. The data carrier is discriminated from reference Gold series used in the correlation calculations of the correlation peak values.

BACKGROUND OF THE INVENTION 
The present invention relates to a system for receiving a transmission 
signal from a data carrier provided for a person, an object, or the like 
located in a building, a factory, or the like and for detecting the 
position where the person or object exists and, more particularly, to a 
system for detecting the position of the person or object by using spread 
spectrum communication. 
In recent years, in association with the progress of the office automation 
or factory automation, it is desired to centrally manage the movements of 
persons or objects in a building and to properly promptly distribute 
information or items. 
For example, in a building system which has recently been proposed, persons 
who enter a building possess ID cards, a managing system of the building 
recognizes the ID cards, thereby always grasping the locations of such 
persons. For instance, the managing system, can automatically transfer a 
received telephone call to a telephone located near a recognized person. 
On the other hand, in response to the use of an apparatus such as a work 
station or the like, the building managing system transmits a user format 
which is peculiar to the recognized person, thereby enabling personal use. 
To realize such a building system, it is required that a communicating 
function such as a data carrier is provided for the ID card, a peculiar ID 
code is transmitted by a radio system, the transmission signal is received 
on the system side, and the ID code and the position are recognized. 
However, a system in which ID cards (data carriers) are provided for ten 
thousand or more persons per building and in which ID code signals are 
transmitted by radio and the positions of all of the persons in the 
building is always recognized has not yet proposed and has not been put 
into practical use at present. 
This is because in a radio wave propagating space such as an inner room of 
a building, a factory, or the like, there exists strong interferences 
caused by the multiple reflections of objects installed in the room and 
thus normal communication can not be expected using the ordinary 
communicating system. Also, the transmission electric power from the ID 
card which is used as a data carrier is extremely weak because of power 
source limitations and a communication quality of a high realiability 
cannot be obtained due to S/N ratio problems. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide an object position detecting 
system which can always recognize positions of a number of persons in a 
room of an office building, a factory, or the like in a real-time manner. 
Another object of the invention is to provide an object position detecting 
system which can always recognize positions of a number of objects in a 
room of an office building, a factory, or the like in a real-time manner. 
Still another object of the invention is to provide an object position 
detecting system in which leaky cables for receiving and transmitting 
radio signals which are transmitted from a data carrier are installed in a 
building. 
Another object of the invention is to provide an object position detecting 
system in which leaky cables are two-dimensionally arranged in a building. 
Another object of the invention is to provide an object position detecting 
system in which pseudo random series are transmitted from data carriers 
and a correlation calculation is executed on a reception side. 
Another object of the invention is to provide an object position detecting 
system using a Gold series as the pseudo random series which are 
transmitted from data carriers. 
According to the invention, a plurality of portable data carriers are first 
prepared and are possessed by,, for instance, persons who enter a 
building. Unique pseudo random series are assigned to the data carriers 
corresponding to ID codes. A carrier signal of a predetermined frequency 
is spread spectrum modulated by the assigned pseudo random series and is 
transmitted. 
On the other hand, on the building side, leaky cables each having a 
predetermined length are two-dimensionally distributed and installed in 
the structure. A frequency converter is connected to one end of each of a 
plurality of leaky cables 12-1 to 12-n each having a predetermined line 
length (L). A spread spectrum signal from the data carrier which has been 
propagated in the leaky cable, is frequency converted into a frequency 
which is unique to the cable. A plurality of leaky cables are commonly 
connected to one transmission cable. The transmission cable is connected 
to a central receiving unit. 
Gold series are used as pseudo random series which are used in the data 
carriers. 
A carrier signal of a frequency which has been spread spectrum modulated by 
the Gold series transmitted from a special data carrier is received by the 
leaky cable near the special data carrier and is transmitted to both end 
sides of the leaky cable. After that, the carrier signal is frequency 
converted into the frequency which is unique to the cable by the frequency 
converter connected to one end of the cable. The converted frequency 
signal is multiplexed to the signal at the other end of the cable and is 
sent to the receiving unit. 
The receiving unit individually demodulates the signal series from the 
frequency modulated reception signals from the transmission cables and 
sequentially executes correlation calculations of each reception signal 
series and the Gold series assigned to the data carrier. As a time 
difference between a time T.sub.1 when a correlation peak value of the 
reception signal series which had been demodulated by the frequency unique 
to the data carrier is obtained by the correlation calculation and a time 
T.sub.2 when a correlation peak value of the reception signal series which 
had been demodulated by the frequency peculiar to the leaky cable is 
obtained, a delay time .DELTA.T is detected as 
EQU .DELTA.T=T.sub.2 -T.sub.1 
The delay time .DELTA.T depends on distances L.sub.1 and L.sub.2 from the 
position on the leaky cable where the data carrier exists to both ends 
E.sub.1 and E.sub.2 of the cable. Now, assuming that a propagating speed 
of the leaky cable is set to C [m/nsec] and a cable length is set to L 
[m], a distance difference .DELTA.L is obtained as follows. 
EQU .DELTA.L=L.sub.2 -L.sub.1 =C.multidot..DELTA.T 
Therefore, the distance L.sub.1 from the end E.sub.1 of the cable is 
obtained as follows. 
EQU L.sub.1 =(L-.DELTA.L)/2 
On the other hand, the data carrier can be discriminated from the reference 
Gold series which have been used in the receiving unit and the correlation 
calculation of the correlation peak values. 
A plurality of leaky cables are not necessarily commonly connected by the 
transmission cables but can also be individually and separately connected 
to the receiving unit through transmission cables. 
Further, the frequency converter is not necessarily connected to one end, 
of each of the leaky cables, but each end of the leaky cable can be 
directly connected to the receiving unit through the transmission cable. 
The above and other objects, features, and advantages of the present 
invention will become more apparent from the following detailed 
description with reference to the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a constructional diagram showing the first embodiment of the 
invention. 
In FIG. 1, reference numerals 12-1, 12-2, . . . , 12-n denote leaky cables 
which are branch-connected through circulators 15 to a transmission cable 
14 which has been led out of a receiving unit 18, respectively. That is, 
the leaky cables 12-1 to 12-n are two-dimensionally arranged like branches 
in which the transmission cable 14 is used as a trunk. One end E.sub.1 of 
each of the leaky cables 12-1 to 12-n is directly connected to the 
transmission cable 14 through the circulator 15. 
On opposite hand, the other ends E.sub.2 of the leaky cables 12-1 to 12-n 
are input-connected to frequency converters 16-1 to 16-n provided for the 
cables, respectively. Outputs of the frequency converters 16-1 to 16-n are 
directly connected to the transmission cable 14 through the circulators 15 
together with the cable ends E.sub.1. 
The transmission cable 14, circulators 15, leaky cables 12-1 to 12-n, and 
frequency converters 16-1 to 16-n are installed along and under the floor 
or along and within the ceiling of a room of, for instance, a building, a 
factory, or the like. The building side of the system is thus constructed 
as mentioned above. 
On the, other hand, data carriers 10-1 and 10-2 as shown in FIG. 1, for 
example, are possessed by persons who enter the building, respectively. 
Gold series G.sub.1 and G.sub.2 each having a predetermined word length as 
one kind of pseudo random series (PN series) have previously been assigned 
to the data carriers 10-1 and 10-2. Therefore, the data carriers 10-1 and 
10-2 spread spectrum modulate a carrier signal of a frequency f.sub.0 
which has been commonly assigned to all of the data carriers by the Gold 
series G.sub.1 and G.sub.2 and transmit the modulated signal, 
respectively. 
FIG. 2 is a block diagram showing an embodiment of a data carrier for 
explaining the data carrier 10-1 in FIG. 1 as an example. 
In FIG. 2, the data carrier 10-1 comprises: an oscillator 20; a multiplier 
22; a frequency division starting circuit 24; a Gold series generator 25; 
a band pass filter 26; and a transmission antenna 28. 
The oscillator 20 generates the carrier signal of the frequency f.sub.0 
(first frequency) which is common to all of the data carrier and applies 
the carrier signal to the multiplier 22. The oscillation output the 
oscillator 20 is also supplied to the frequency division starting circuit 
24. Frequency division pulses which have been frequency divided at a 
predetermined frequency dividing ratio are supplied from the starting 
circuit 24 to the Gold series generator 25. 
The Gold series generator 25 generates the Gold series G.sub.1 of a 
predetermined word length which has previously been assigned. It is known 
that the Gold series are codes which are generated by using M series as a 
preferred pair. The preferred pair denotes a combination of M series which 
uniformly have small cross-correlation values. Thus, when correlation 
values (cross-correlation values) of different Gold series are calculated, 
a small cross-correlation value which is certainly uniform is assured in 
any case and an S/N ratio in the case where an autocorrelation has been 
derived can be guaranteed. 
On the other hand, although the kind of Gold series which can be assigned 
to the data carrier is determined by the word length of the Gold series, 
about a hundred thousand different Gold series can be assigned so long as 
the maximum word length of the Gold series which has been found out until 
now is used. Thus, a hundred thousand data carriers can be discriminated 
and prepared per building or facility. 
The Gold series G.sub.1 of a predetermined word length is generated from 
the Gold series generator 25 synchronously with the frequency division 
pulses from the frequency division starting circuit 24 every predetermined 
period. The Gold series G.sub.1 has a time sequence of chip components 
comprising bits 1 or 0 corresponding to the word length for a series time 
duration T as shown in, for instance, FIG. 3. Bit 1 corresponds to the 
signal of +1 and bit 0 corresponds to the signal of -1. A period of one 
chip component is shown by a chip period .DELTA.T.sub.c. 
The Gold series G.sub.1 from the Gold series generator 25 is multiplied to 
the carrier signal of the frequency f.sub.0 from the oscillator 20 by the 
multiplier 22. The frequency f.sub.0 of the carrier signal has a carrier 
period which is a fraction of an integer of the chip period .DELTA.T.sub.c 
of the Gold series in FIG. 3. In the case of FIG. 3, the frequency f.sub.0 
is set to half the chip period .DELTA.T.sub.c. The multiplier 22 
multiplies the Gold series and the carrier signal, thereby producing a 
spread spectrum signal (phase modulation signal) in which a phase of the 
carrier signal is inverted when the Gold series changes from +1 to -1 or 
from -1 to +1 as shown in FIG. 3. The spread spectrum signal from the 
multiplier 22 is band limited by the band pass filter 26 and, thereafter, 
it is transmitted from the transmission antenna 28. 
A transmission electric power from the data carrier 10-1 is extremely weak 
because a power source such as a solar battery or the like is used. A 
transmission electric power, it is sufficient to use a very weak 
transmission electric power may be used which is sufficient to assure an 
effective propagation distance of about 2 m in consideration of the 
installation intervals and installation positions of the leaky cables 12-1 
to 12-n shown in FIG. 1. 
Returning to FIG. 1, in the embodiment, the diagram shows the case where a 
person who possesses the data carrier 10-1 to which the Gold, series 
G.sub.1 has previously been assigned is located near the leaky cable 12-2 
and a person who possesses the data carrier 10-2 to which the Gold series 
G.sub.2 has previously been assigned is located between the leaky cables 
12-1 and 12-3. 
As shown by the example of FIG. 4, each of the frequency converters 16-1 to 
16-n connected to the leaky cables 12-1 to 12-n or the like comprises: a 
high frequency amplifier 54; a mixer 56; a shift frequency oscillator 58; 
and a band pass filter 60. 
That is, a propagation signal due to the reception of the spread spectrum 
signal of the frequency f.sub.0 from the data carrier 10-2 near the leaky 
cable 12-1 in FIG. 1 is supplied to the frequency converter 16-1 and is 
amplified by the high frequency amplifier 54. After that, the amplified 
signal is given to the mixer 56. An oscillation output of a frequency 
(f.sub.1 - f.sub.0) is given to the other input terminal of the mixer 56 
from the shift frequency oscillator 58 and is mixed into the spread 
spectrum signal of the frequency f.sub.0. Thus, the signal of the spread 
center frequency f.sub.0 is frequency converted into the signal of the 
spread center frequency f.sub.1 which is unique to the leaky cable 12-1 as 
shown in FIG. 5. Finally, an output signal of the mixer 56 is band limited 
by the band pass filter 60 having the center frequency f.sub.1 and, after 
that, it is transmitted to the receiving unit 18. 
Each of the other frequency converters 16-2 to 16-n has the same 
construction as that of the frequency converter 16-1 shown in FIG. 4. 
Since frequencies f.sub.2 to f.sub.n which are unique to the leaky cables 
12-2 to 12-n are set for the frequency converters 16-2 to 16-n, frequency 
signals of (f.sub.2 - f.sub.0) to (f.sub.n - f.sub.0) are oscillated from 
the oscillator 58 and are frequency converted. 
FIG. 6 is a block diagram showing an embodiment of the receiving unit 18 
shown in FIG. 1. 
In FIG. 6, the receiving unit 18 comprises: a data carrier correspondence 
receiving section 18-0 corresponding to the data carrier; and cable 
correspondence receiving sections 18-1 to 18-n corresponding to the leaky 
cables 12-1 to 12-n. 
The data carrier correspondence receiving section 18-0 comprises: a high 
frequency amplifier 32; a band pass filter 34-0 of the center frequency 
f.sub.0 ; a demodulator 36 having a local oscillator 46-0 of the 
oscillating frequency f.sub.0 ; a low pass filter 38; an A/D converter 40 
having an oscillator 48 which oscillates a sampling frequency f.sub.s ; a 
buffer memory 42; and a correlator 44 using a DSP. 
On the other hand, the cable correspondence receiving sections 18-1 to 18-n 
have substantially the same circuit construction as that of data carrier 
correspondence receiving section 18-0 except that center frequencies of 
band pass filters 34-1 to 34-n are set to the frequencies f.sub.1 to 
f.sub.n which are unique to the cables and that oscillating frequencies of 
local oscillators 46-1 to 46-n for the demodulator 36 are set to the 
frequencies f.sub.1 to f.sub.0 unique to the cables. 
Further, a plurality of Gold series G.sub.1 to G.sub.m which have been 
commonly assigned to all of the data carriers are sequentially commonly 
given as reference Gold series from a Gold series generator 50 to the 
correlators 44 provided in the receiving sections 18-0 to 18-n. Therefore, 
the correlator 44 calculates a correlation between the reception series 
from the buffer memory 42 and the reference Gold series from the Gold 
series generator 50, that is, calculates a product sum for every data of 
one series length which is decided by the sampling period of the A/D 
converter 40. 
Correlation outputs C.sub.0 to C.sub.n of the correlators 44 provided in 
the receiving sections 18-0 to 18-n are given to a processor 52. The 
processor 52 stores times when peak values of the correlation outputs 
C.sub.0 to C.sub.n have been derived into latches T.sub.1 and T.sub.2, 
respectively. Namely, the peak value detection time of the correlation 
output C.sub.0 from the data carrier correspondence receiving section 18-0 
is stored into the latch T.sub.1. On the other hand, the peak value 
detection time from either one of the correlation outputs C.sub.1 to 
C.sub.n of the cable correspondence receiving sections 18-1 to 18-n is 
stored into the latch T.sub.2. On the basis of the peak detection times in 
the latches T.sub.1 and T.sub.2, the processor 52 calculates the distance 
L.sub.1 from the cable end E.sub.1 on the side of the circulator 15 to a 
reception point A of the transmission signal from the data carrier 10-1 in 
the case of, for instance, the leaky cable 12-2 in FIG. 1. The processor 
52 also recognizes the data carrier on the basis of the Gold series from 
the Gold series generator 50 which has been used to calculate the 
correlation peak values for the time detection of the latches T.sub.1 and 
T.sub.2. 
The operation of the receiving unit 18 in FIG. 6 will now be described in 
detail. 
It is now assumed that a person who possesses the data carrier 10-1 is 
located near the leaky cable 12-2 in FIG. 1. When the spread spectrum 
signal having the frequency f.sub.0 is transmitted from the data, carrier 
10-1, the signal is received at the A point of the leaky cable 12-2. The 
reception signal is propagated from the A point toward the cable ends 
E.sub.1 and E.sub.2 on both sides of the leaky cable 12-2. A propagation 
signal which has reached the cable end E.sub.1 is sent to the receiving 
unit 18 through the circulator 15 and the transmission cable 14. 
On the other hand, a propagation signal which has reached the cable end 
E.sub.2 is frequency converted into the signal of the frequency f.sub.2 
unique to the leaky cable 12-2 by the frequency converter 16-2 and is sent 
to the receiving unit 18. 
Therefore, one series of the spread spectrum signal of the frequency 
f.sub.0 and one series of the frequency converted spread spectrum signal 
of the frequency f.sub.2 are received by the receiving unit 18 in order 
according to a difference between the distances from both cable ends to 
the reception point A. 
The spread spectrum signal of the frequency f.sub.0 is amplified by the 
high frequency amplifier 32 in the data carrier correspondence receiving 
section 18-0 and, after that, the amplified signal passes through the band 
pass filter 34-0 having the center frequency f.sub.0 and is demodulated 
into the reception signal series of the base band by the demodulator 36. 
Further, after the signal is transmitted through the low pass filter 38, 
it is converted into the digital data by the A/D converter 40 and is 
stored into the buffer memory 42. The sampling frequency f.sub.s in the 
A/D converter 40 is determined to a value such that the data can be 
sampled a plurality of times of two or more times for the chip period 
.DELTA.T.sub.c of the Gold series in FIG. 3. 
On the other hand, the spread spectrum signal of the frequency f.sub.2 
which has been subjected to the frequency shift is extracted by the band 
pass filter 34-2 in the cable correspondence receiving section 18-2 
corresponding to the leaky cable 12-2. The extracted signal is likewise 
demodulated to the reception signal series of the base band by the 
frequency f.sub.2 from the local oscillator 46-2 and, thereafter, the 
demodulated signal is stored as digital data into the buffer memory 42 in 
a manner similar to the case of the data carrier correspondence receiving 
section 18-0. 
The correlators 44 in the data carrier correspondence receiving section 
18-0 and the cable correspondence receiving section 18-2 read out the 
reception signal series stored in the buffer memories 42 and execute 
correlation calculations (product sum calculations) between the read-out 
reception signal series and the reference Gold series G.sub.1 to G.sub.m 
which are sequentially given from the Gold series generator 50 at that 
time. When the reference Gold series from the Gold series generator 50 
assume G.sub.1, they are the same series as the reception signal series, 
so that correlation peak values are obtained in the correlation outputs 
C.sub.0 and C.sub.2 of the correlators 44. 
That is, since the reception point A of the transmission signal from the 
data carrier 10-1 to the leaky cable 12-2 in FIG. 1 is close to the cable 
end E.sub.1 is far from the cable end E.sub.2, as shown in FIG. 8A, the 
signal series of the frequency f.sub.0 are first received. After the 
elapse of the delay time .DELTA.T corresponding to the difference between 
distances from both cable ends to the reception point A, the reception of 
the signal series which have been frequency converted into the frequency 
f.sub.2 shown in FIG. 8B is started. In the data carrier correspondence 
receiving section 18-0, if it is assumed that the correlation calculations 
were executed in a real-time manner, a peak value occurs in the 
correlation output C.sub.0 shown in FIG. 8C at time t.sub.1 when the 
reception of the signal series of the f.sub.0 signal has been finished. 
The time t.sub.1 is stored into the latch T.sub.1. Subsequently, as shown 
in FIG. 8D, a peak value is obtained in the correlation output C.sub.2 at 
time t.sub.2 by the correlation calculation regarding the signal series of 
the f.sub.2 signal. The second peak value detection time t.sub.2 is stored 
into the latch T.sub.2. 
The peak generation times t.sub.1 and t.sub.2 are not detected in a 
real-time manner, but, for instance, values of write addresses of the 
series final data when the series data is written into the buffer memory 
42 are obtained as times t.sub.1 and t.sub.2. 
When the peak value generation times t.sub.1 and t.sub.2 of the correlation 
outputs C.sub.0 and C.sub.2 are detected by the processor 52 as mentioned 
above, the processor 52 first calculates the delay time .DELTA.T as 
follows. 
EQU .DELTA.T=T.sub.2 -T.sub.1 =t.sub.2 -t.sub.1 
As shown in FIG. 7 showing the leaky cable 12-2 in FIG. 1, it is now 
assumed that a length of leaky cable 12-2 is set to L, a distance from the 
cable end E.sub.1 to the reception point A is set to L.sub.1, a distance 
from the cable end E.sub.2 to the reception point A is set to L.sub.2, and 
a propagating speed of the signal in the leaky cable 12-2 is set to C 
[m/nsec]. 
As will be obviously understood from the distance relation for the 
reception point A in FIG. 7, the processor 52 calculates a distance 
difference .DELTA.L between the propagation distances L.sub.1 and L.sub.2 
on both cable ends to the reception point A as follows by using the delay 
propagation time .DELTA.T and the cable delay propagating speed C. 
EQU .DELTA.L=L.sub.2 -L.sub.1 =C.multidot..DELTA.T (1) 
As will be obviously understood from FIG. 7, there is the following 
relation. 
EQU L=L.sub.1 +L.sub.2 (where, L.sub.1 &lt;L.sub.2) 
By solving the simultaneous equations with the above equation (1), the 
distance L.sub.1 from the cable end E.sub.1 to the reception point A is 
calculated as follows. 
EQU L.sub.1 =(L-.DELTA.L)/2 (2) 
Further, the processor 52 recognizes the data carrier on the basis of the 
reference Gold series from the Gold series generator 50 which have been 
used for the calculations of the peak value in the correlation output 
C.sub.0 and the peak value in either one of the correlation outputs 
C.sub.1 to C.sub.m. In this case, since the peak value of the correlation 
output has already been obtained by the reference Gold series G.sub.1, the 
data carrier 10-1 to which the Gold series G.sub.1 has been assigned can 
be recognized. 
When the distance L.sub.1 from the end E.sub.1 of the leaky cable 12-2 to 
the reception point A and the data carrier 10-1 are recognized, since the 
position of the leaky cable 12-2 in the building has previously been known 
on the processor 52 side, the fact that the data carrier exists at the A 
point of the calculated distance L.sub.1 in the building is informed to 
the higher order apparatus, thereby allowing necessary processes to be 
executed. 
FIG. 9 is an explanatory diagram showing another two-dimensional 
arrangement of a leaky cable which is used in the invention. The 
embodiment is characterized in that the leaky cable 12-1 is spirally 
arranged as a leaky cable which is connected like a branch to the 
transmission cable 14 through the circulator 15 as shown in the case of 
the leaky cable 12-1 as a typical example. A cable installation density 
can be raised and the position detecting accuracy can be improved by such 
a spiral arrangement of the leaky cable 12-1. The spiral shape of the 
leaky cable 12-1 is not limited to a rectangle as shown in the diagram, 
but can be also set to a proper spiral shape such as circle, ellipse, or 
the like. 
In the embodiment of FIG. 1, the leaky cable side has been connected to the 
transmission cable 14 through the circulator 15. However, the leaky cables 
12-1 to 12-n can also be directly connected to the transmission cable by 
eliminating the circulators 15. 
In the case where the position of the data carrier 10-2 has been detected 
by both of the leaky cables 12-1 and 12-3 in FIG. 1, it is recognized that 
the data carrier 10-2 exists at an intermediate point of a straight line 
connecting both of the detection positions. 
Further, in the embodiment, although the distance L.sub.1 from the cable 
end E.sub.1 has been detected, the distance L.sub.2 from the cable end 
E.sub.2 can be also detected on the contrary. 
Moreover, the frequency converters 16-1 to 16-n can be also provided on the 
side of the cable end E.sub.1. 
FIG. 10 is a constructional diagram showing the second embodiment of the 
invention. The embodiment is characterized in that the leaky cables 12-1 
to 12-n are individually connected to the receiving unit 18. 
In FIG. 10, the leaky cables 12-1 to 12-n are distributed and arranged like 
branches along and just under the floor or along the ceiling in the room 
of a building, a factory, or the like. Cable ends E.sub.1 of the leaky 
cables 12-1 to 12-n are input-connected to the frequency converters 16-1 
to 16-n. The transmission cables 14 are led out of the other ends E.sub.2 
of the leaky cables 12-1 to 12-n, respectively. The outputs of the 
frequency converters 16-1 to 16-n are connected to the transmission cable 
14. The transmission cables 14 led out of the leaky cables 12-1 to 12-n 
are connected to the receiving unit 18. 
On the other hand, the data carriers shown in FIG. 2 are used as data 
carriers 10-1 and 10-2. The frequency converters shown in FIG. 4 are also 
used as frequency converters 16-1 to 16-n. 
FIG. 11 is a block diagram showing an embodiment of the receiving unit 18 
in FIG. 10. 
In FIG. 11, receiving sections 118-1 to 118-n are provided in the receiving 
unit for 18 every leaky cables 12-1 to 12-n. In the embodiment, a 
construction of the receiving section 118-1 corresponding to the leaky 
cable 12-1 is practically shown as a typical example. 
A first receiving system 130-1 and a second receiving system 130-2 are 
provided for the receiving section 118-1. The transmission cable 14 from 
the leaky cable 12-1 is input-connected to those systems in parallel. 
The first receiving system 130-1 comprises: a high frequency amplifier 
132-1; a band pass filter 134-1 having the center frequency f.sub.1 ; a 
demodulator 136-1; a local oscillator 146-1 having the oscillating 
frequency f.sub.1 ; a low pass filter 138-1; an A/D converter 140-1; a 
buffer memory 142-1; and a correlator 144-1 using a DSP. 
On the other hand, the second receiving system 130-2 comprises: a high 
frequency amplifier 132-2; a band pass filter 134-2 having the center 
frequency f.sub.2 ; a demodulator 136-2; a local oscillator 146-2 having 
the oscillating frequency f.sub.2 ; a low pass filter 138-2; an A/D 
converter 140-2; a buffer memory 142-2; and a correlator 144-2 using a 
DSP. 
Further, as a common circuit section for the first and second receiving 
systems 130-1 and 130-2, an oscillator 148 for oscillating the sampling 
frequency f.sub.s is provided for the A/D converters 140-1 and 140-2. The 
Gold series generator 50 for generating the Gold series G.sub.1 to G.sub.m 
for all of the data carriers by sequentially switching them is also 
provided for the correlators 144-1 and 144-2. 
The operation of the receiving section 18-1 will now be described 
hereinbelow. 
First, it is now assumed that the spread spectrum signal of the center 
frequency f.sub.1 has been received from the leaky cable 12-1 through the 
transmission cable 14. After the signal is amplified by the high frequency 
amplifier 132-1, it passes through the band pass filter 134-1 and the 
signal of the base band indicative of the Gold series is demodulated by 
the demodulator 136-1 by using the oscillating signal of the frequency 
f.sub.1 from the local oscillator 146-1. Practically speaking, the 
demodulator 136-1 can be realized by a demodulating circuit of a two-phase 
modulation signal. The reception signal series of the base band which have 
been demodulated by the demodulator 136-1 pass through the low pass filter 
138-1 and, thereafter, they are sampled by the A/D converter 140-1 by the 
sampling frequency f.sub.s from the oscillator 148. A sampling period at 
this time is determined to be a period which is equal to or shorter than 
the half of the chip period .DELTA.T.sub.c in the Gold series shown in 
FIG. 3. 
The reception signal series converted into the digital data by the A/D 
converter 140-1 are stored into the buffer memory 142-1. Each data memory 
address of the reception signal series of at least one series stored in 
the buffer memory 142-1 indicates a reception time. After the reception 
signal series of one series are stored into the buffer memory 142-1, they 
are read out to the correlator 144-1. The correlator 144-1 executes the 
correlation calculation every reference series by using the Gold series 
G.sub.1 to G.sub.m which are sequentially given from the Gold series 
generator 50 and have been assigned to all of the data carriers as 
reference series. 
If the reception signal series and the reference series from the Gold 
series generator 50 coincide as a result of the correlation calculations, 
a peak value appears in the correlation output C.sub.1 of the correlator 
144-1. 
The processor 52 recognizes the time when the peak value of the correlation 
output C.sub.1 has been derived on the basis of the memory addresses of 
the reception signal series in the buffer memory 142-1. Further, the 
processor 52 can recognize the data carrier which has transmitted the 
spread spectrum signal on the basis of the reference Gold series generated 
from the Gold series generator 50 when the peak value had been obtained. 
The second receiving system 130-2 is substantially the same as the first 
receiving system 130-1 except that the center frequency of the band pass 
filter 134-2 is set to f.sub.2 and that the oscillating frequency from the 
local oscillator 146-2 to the demodulator 136-2 is likewise set to 
f.sub.2. That is, on the side of the second receiving system 130-2, the 
signal from the cable end E.sub.1 of the leaky cable 12-1 in FIG. 10 is 
frequency converted into the spread frequency f.sub.2 by the frequency 
converter 116-1 and is transmitted, the transmitted signal is received and 
demodulated, the correlation calculations with the reference Gold series 
G.sub.1 to G.sub.m are finally executed by the correlator 144-2, and the 
processor 52 recognizes the data carrier from the reference Gold series 
used in the calculation of the peak value of the correlation output 
C.sub.2. 
On the basis of the peak value detection times t.sub.1 and t.sub.2 of two 
correlation outputs C.sub.1 and C.sub.2 shown in FIGS. 8A to 8D, the 
processor 52 calculates the distance L.sub.1 from the end E.sub.1 of the 
leaky cable 12-2 to the reception point A as shown in FIG. 7. 
The entire operation of the embodiment of FIG. 10 will now be explained. 
Now, assuming that a person who possesses the data carrier 10-1 is located 
near the leaky cable 12-2 as shown in FIG. 10, the periodic spread 
spectrum signal is transmitted from the data carrier 10-1 and is received 
at the reception point A of the leaky cable 12-2. The signal received at 
the reception point A progresses toward the cable ends E.sub.1 and 
E.sub.2. The transmission signal which has reached the cable end E.sub.1 
is frequency converted from the spread center frequency f.sub.1 to another 
spread center frequency f.sub.2 by the frequency converter 16-2 and is 
given to the receiving unit 18 by the transmission cable 14 together with 
the signal of the spread center frequency f.sub.1 which has already been 
transmitted to the cable end E.sub.2 by the transmission cable 14. 
In the receiving unit 18, the reception signal series of the frequency 
f.sub.1 are demodulated by the first receiving system 130-1 in the 
receiving section 18-2 in FIG. 11 provided in correspondence to the leaky 
cable 12-2. The reception signal series of the frequency f.sub.2 are also 
demodulated by the second receiving system 130-2. After the demodulation 
signals of the above series were converted into the digital data, they are 
supplied to the correlators 144-1 and 144-2 and the correlation 
calculations with the Gold series G.sub.1 to G.sub.m from the Gold series 
generator 50 are sequentially executed. 
Since the data carrier 10-1 has the Gold series G.sub.1, the peak values 
are obtained in accordance with the order of the correlation outputs 
C.sub.1 and C.sub.2 as shown in FIGS. 8C and 8D by the correlation 
calculations with the reference Gold series G.sub.1. The processor 52 
calculates the delay time .DELTA.T as follows. 
EQU .DELTA.T=t.sub.2 -t.sub.1 
Then, the processor 52 obtains the distance difference .DELTA.L from the 
equation (1) and calculates the distance L.sub.1 from the cable end 
E.sub.1 to the reception point A by the equation (2). 
The processor 52 further recognizes the data carrier 10-1 from the 
reference Gold series G.sub.1 used in the correlation calculations of the 
correlation outputs C.sub.1 and C.sub.2 at which the peak values have been 
obtained. 
Since the position of the leaky cable 12-2 in the building is previously 
known, the position of the data carrier 10-1 in the building is recognized 
on the basis of the calculated distance L.sub.1 and is informed to the 
higher order apparatus, thereby allowing proper processes to be performed. 
Further, in the case where the position of the data carrier 10-2 in FIG. 10 
has been detected by both of the leaky cables 12-1 and 12-3, it is 
recognized that the data carrier 10-2 exists at an intermediate position 
of a line connecting the reception point A which is decided by the 
distance L.sub.1 from each of the cable end E.sub.1 of the leaky cables 
12-1 and 12-3. 
FIG. 12 is an explanatory diagram, showing another two-dimensional 
arrangement of a leaky cable which is used in the embodiment of FIG. 10 
and is characterized in that a leaky cable 12 is spirally arranged like a 
rectangle in a manner similar to the case of FIG. 9. The cable 
installation density can be raised and the position detecting accuracy can 
be improved by such a spiral arrangement of the leaky cable 12. The shape 
of the leaky cable 12 is not limited to the rectangular spiral shape, but 
can be set to a proper spiral shape of a circle, an ellipse, or the like. 
In the embodiment of FIG. 10, although the signals from the cable ends 
E.sub.1 of the leaky cables 12-1 to 12-n have been frequency converted and 
transmitted, the signals from the cable ends E.sub.2 on the opposite side 
can be also frequency converted. 
FIG. 13 is a constructional diagram showing the third embodiment of the 
invention. The embodiment is characterized in that the frequency 
converters 16-1 to 16-n provided for the leaky cables 12-1 to 12-n are 
unnecessary. 
In FIG. 13, the leaky cables 12-1 to 12-n are distributed and arranged like 
branches along and just under the floor or along the ceiling in the room 
of, for example, a building, a factory, or the like as shown in the 
diagram. 
The transmission, cables 14 are connected to both ends of each of the leaky 
cables 12-1 to 12-n, respectively. Each of the two transmission cables 
from each of the leaky cables 12-1 to 12-n is connected to the receiving 
unit 18. 
On the other hand, the data carriers 10-1 and 10-2 are possessed by persons 
who enter the building, for instance, as shown in the diagram. Data 
carriers as shown in FIG. 2 are used as data carriers 10-1 and 10-2. 
FIG. 14 shows an embodiment of the receiving unit 18 in FIG. 13. 
In FIG. 14, independent receiving sections 218-1 to 218-n are provided in 
the receiving unit 18 for each of the leaky cables 12-1 to 12-n. 
A construction of the receiving section 218-1 corresponding to the leaky 
cable 12-1 is shown as a typical example. 
The receiving section 218-1 comprises: a first receiving system 230-1 to 
which, the transmission cable 14 from one end E.sub.1 of the leaky cable 
12-1 in FIG. 13 is input-connected; and a second receiving system 230-2 to 
which the transmission cable 14 from the other end E.sub.2 of the leaky 
cable 12-1 is input-connected. 
The first receiving system 230-1 comprises: a high frequency amplifier 
232-1; a band pass filter 234-1; a demodulator 236-1; a low pass filter 
238-1; an A/D converter 240-1; a buffer memory 242-1; and a correlator 
244-1 using a DSP. The second receiving system 230-2 also similarly 
comprises: a high frequency amplifier 232-2; a band pass filter 234-2; a 
demodulator 236-2; a low pass filter 238-2; an A/D converter 240-2; a 
buffer memory 242-2; and a correlator 244-2. As a common circuit section 
of the above receiving systems, a local oscillator 246 for oscillating the 
frequency f.sub.1 is provided for the demodulators 236-1 and 236-2. A 
sampling oscillator 248 for oscillating the sampling frequency f.sub.s is 
commonly provided for the A/D converters 240-1 and 240-2. Further, the 
Gold series generator 50 for sequentially generating a plurality of Gold 
series G.sub.1 to G.sub.m which have previously been assigned to the data 
carriers as reference series is provided for the correlators 244-1 244-2. 
The processor 52 is connected after the receiving section 218-1. The 
correlation outputs C.sub.1 and C.sub.2 of the correlators 244-1 and 244-2 
are given to the processor 52. As shown in, for example, FIGS. 8C and 8D, 
when the peak value is first given from the correlation output C.sub.1 of 
the correlator 244-1, the processor 52 latches the peak value generating 
time t.sub.1 and subsequently monitors the correlation output C.sub.2 on 
the side of the correlator 244-2 and latches the time t.sub.2 when the 
peak value is then obtained. 
If two correlation peak values are continuously obtained from the 
correlation outputs of the correlators 244-1 and 244-2, the processor 52 
calculates the delay time .DELTA.T as a difference between the peak value 
detecting times. On the basis of the delay time .DELTA.T, the processor 52 
calculates the distance L.sub.1 from the cable end E.sub.1 to the 
reception point A in a manner similar to the case shown in FIG. 7 with 
respect to, for instance, the leaky cable 12-2 which has received the 
signal from the data carrier 10-1 in FIG. 13. 
The operation of the embodiment in FIG. 13 will now be described. 
It is now assumed that a person who possesses the data carrier 10-1 is 
located near the leaky cable 12-2 as shown in FIG. 13. The spread spectrum 
signal (frequency f.sub.1) which has been spread spectrum modulated in 
accordance with the Gold series G.sub.1 which had previously been assigned 
is transmitted from the data carrier 10-1 and is received at the A point 
of the leaky cable 12-2. The reception signal at the A point propagates in 
the leaky cable 12-2 toward the cable ends E.sub.1 and E.sub.2. Since 
there is the following relation between the distances from the cable ends 
E.sub.1 and E.sub.2 to the reception point A 
EQU L.sub.1 &lt;L.sub.2 
the transmission signal which has propagated toward the cable end E.sub.1 
first reaches the cable end E.sub.1 and thereafter the transmission signal 
which has propagated in the opposite direction reaches the cable end 
E.sub.2. Thus, on the receiving unit 18 side, the spread spectrum signal 
of one word length from the cable end E.sub.1 side is first received and 
the spread spectrum signal of one word length from the cable end E.sub.2 
is subsequently received. 
As shown in FIG. 14, in the receiving unit 18, the reception signals from 
the cable ends E.sub.1 and E.sub.2 are demodulated by the demodulators 
236-1 and 236-2 in the receiving section 218-2 corresponding to the 
leakage cable 12-2. After that, the demodulated signals are converted into 
the digital data by the A/D converters 240-1 and 240-2 and stored into the 
buffer memories 242-1 and 242-2. The reception series signals of one word 
length stored in the buffer memories 242-1 and 242-2 are given to the 
correlators 244-1 and 244-2. Addresses in the buffer memories 242-1 and 
242-2 correspond to the receiving times, so that the receiving times can 
be known from the addresses in the buffer memories. 
The reception signal series of one word length stored in the buffer 
memories 242-1 and 242-2 are given to the correlators 244-1 and 244-2 and 
the correlation calculations between the reception signal series and the 
Gold series G.sub.1 to G.sub.m which are sequentially generated from the 
Gold series generator 50 and have previously been assigned to the data 
carriers are sequentially executed. The correlation calculations 
correspond to the product sum calculations between the reception signal 
series and the reference series which are given from the Gold series 
generator 50. 
When the correlation calculations using the Gold series G.sub.1 assigned to 
the data carrier 10-1 as reference series are executed by the correlators 
244-1 and 244-2, as shown in FIGS. 8C and 8D, the peak value corresponding 
to the time t.sub.1 is obtained in the correlation output C.sub.1 of the 
correlator 244-1 and the correlation peak value corresponding to the time 
t.sub.2 is derived in the correlation output C.sub.2 of the correlator 
244-2. 
The processor 52 calculates the delay time .DELTA.T from the times t.sub.1 
and t.sub.2 when the correlation peak values in the correlation outputs 
C.sub.1 and C.sub.2 have been derived. Further, the processor 52 obtains 
the distance difference .DELTA.L from the equation (1). 
In the leaky cable 12-2 in FIG. 1, since there is the following relation 
between the distances L.sub.1 and L.sub.2 to the reception point A 
EQU L.sub.1 &lt;L.sub.2 
the delay time .DELTA.T has a plus value. Therefore, by substituting the 
distance difference .DELTA.L calculated by the equation (1) into the 
equation (2), the distance L.sub.1 from the cable end E.sub.1 to the 
reception point A is calculated. 
Since the position of the cable end E.sub.1 of the leaky cable 12-2 in the 
building is previously known on the processor 52 side, if the distance 
L.sub.1 is derived, the position in the building where the data carrier 
10-1 exists can be known. In addition, to obtain the correlation peak 
values, the Gold series generator 50 gives the Gold series G.sub.1 to the 
correlators 244-1 and 244-2 as reference series. Therefore, by recognizing 
the reference Gold series by the processor 52 side, the data carrier 10-1 
can be recognized. 
Therefore, the fact that the data carrier 10-1 exists at the position of 
the distance L.sub.1 from the cable end E.sub.1 of the leaky cable 12-2 
installed in the building is informed to a higher order apparatus or the 
like by the processor 52, thereby allowing necessary processes to be 
executed. 
Further, as shown on the sides of the leaky cables 12-1 and 12-3 in FIG. 
13, if the position of the data carrier 10-2 has been detected by both of 
the leaky cables 12-1 and 12-3, it is possible to recognize that the data 
carrier 10-2 exists at an intermediate position of a line connecting the 
positions which are decided by the distances L.sub.1 from the ends E.sub.1 
of the leaky cables 12-1 and 12-3. 
FIG. 15 is an explanatory diagram showing another two-dimensional 
arrangement of a leaky cable used in FIG. 13. The embodiment is 
characterized in that the leaky cable 12 is spirally arranged like a 
rectangle and the transmission cables 14 are led out of the cable ends 
E.sub.1 and E.sub.2, respectively. The shape of the leaky cable 12 is not 
limited to the rectangular spiral shape, but can be also set to a proper 
spiral shape of a circle, an ellipse, or the like.