US 12,265,166 B1 · Method and system for acoustic indoor positioning based on CDMA

Abstract

The invention discloses a method for acoustic indoor positioning based on CDMA, which comprises: generating a BPSK signal; The BPSK signal was detected, the collected signal was de-carrierized and low-pass filtered, and then the data was down-sampled to the design code rate, and then the coarse position of the identification code was determined by the prefix code. Finally, the data with the same length as the identification code was intercepted from the data for matching filtering through the coarse position. Four base stations were designed in each area to obtain three TDOA observations generated by four TOA information, and the terminal position could be obtained through the three TDOA observations. Different areas are distinguished by different identification codes to achieve wide area coverage. The invention provides an effective means for accurate positioning in an indoor environment.

A method for acoustic indoor positioning based on code division multiple access (CDMA), which comprises:

generating a binary phase shift keying (BPSK) signal, after mapping a signal number, a code is upsampled to a sampling frequency of a digital-to-analog converter (DAC), and then an up-sampled signal is passed through a shaping filter;
Finally, a filtered whole signal is multiplied by a carrier signal to offset a center frequency of the filtered whole signal to a carrier frequency;
detecting the BPSK signal;
wherein detecting the BPSK signal comprises:
after de-carrier processing, a collected signal is low-pass filtered, and then a filtered data is down-sampled to a design code rate, and then a coarse position of an identification code is determined by a prefix code;
Finally, through the coarse position, data with the same length as the identification code is intercepted from the data for matching filtering, and a time of arrival (TOA) of the BPSK signal is obtained;
designing four base stations for each area, three time difference of arrival (TDOA) observations generated by four TOA information are obtained, and a terminal position can be obtained through the three TDOA observations;
different areas are distinguished by different identification codes to achieve wide area coverage;
detecting the BPSK signal further comprises:
preprocessing the BPSK signal, which comprises:
After an acoustic signal propagates through the air, after time τ, a microphone of the terminal collects a broadcast signal;
it can be considered that a collected signal has gone through channel attenuation and is doped with environmental noise, which is denoted as:
R
⁡
(
t
+
τ
)
=
Hs
⁡
(
t
)
+
n
⁡
(
t
+
τ
)
=
AHx
⁡
(
t
)
⁢
cos
⁡
(
2
⁢
π
⁢
f
c
⁢
t
)
+
n
⁡
(
t
+
τ
)
;
wherein, A is an amplitude, fc is the carrier frequency, x(t) is an actual transmitted signal, and s(t) is an original signal of the base station, n(t) is an environmental noise, H is a channel attenuation amplitude;
the collected signal is multiplied by the carrier signal;
a process is called de-carrier and is denoted as:
R
⁡
(
t
+
τ
)
⁢
cos
⁡
(
2
⁢
π
⁢
f
c
⁢
t
)
=
AHx
⁡
(
t
)
⁢
cos
2
(
2
⁢
π
⁢
f
c
⁢
t
)
+
n
⁡
(
t
+
τ
)
⁢
cos
⁡
(
2
⁢
π
⁢
f
c
⁢
t
)
=
1
2
⁢
A
⁢
H
⁢
x
⁡
(
t
)
+
1
2
⁢
A
⁢
H
⁢
x
⁡
(
t
)
⁢
cos
⁡
(
4
⁢
π
⁢
f
c
⁢
t
)
+
n
⁡
(
t
+
τ
)
⁢
cos
⁡
(
2
⁢
π
⁢
f
c
⁢
t
)
;
a signal part transmitted by a loudspeaker is decomposed from a received signal, and then a result signal part is filtered by a low-pass filter to remove an irrelevant high-frequency information in the signal part, suppress the noise in the environment and an interference of other signals to obtain x(t), which is denoted as:
LPF
[
R
⁡
(
t
+
τ
)
⁢
cos
⁡
(
2
⁢
π
⁢
f
c
⁢
t
)
]
=
1
2
⁢
A
⁢
H
⁢
x
⁡
(
t
)
;
Then, the data is downsampled to compress the signal x(t) from the sampling frequency to a design-time code rate;
confirming the TOA upon arrival:
Because the prefix code is a head of the identification code, a position of the prefix code is found by a simple front-back matching in the time domain, and the coarse position of the identification code is determined;
Through the coarse position, the data with the same length as the identification code is intercepted from the data for matched filtering;
before the matched filtering, the frequency offset was processed;
performing Fourier transform on an intercepted signal, and then a transformed signal was converted from a time domain to a frequency domain;
at this time, a frequency point where a strength of a frequency domain maximum value is located is the frequency offset of a converted signal;
these alternative frequency offsets are de-carriered with the intercepted signal by enumeration, and then matched with a template of the identification code to confirm the TOA of the BPSK signal when it arrives;
wherein, a generated BPSK signal comprises:
a design of a signal number composed of a pre-buffer code, a prefix code, an identification (ID) code and a post-buffer code, the identification code is randomly generated by a Gold sequence, the prefix code is a part of a tail of a copy identification code, the pre-buffer code and the post-buffer code are random values of 0 to 1 multiplied by a window function, and the pre-buffer code and the post-buffer code are of an equal length.

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Method and system for acoustic indoor positioning based on CDMA

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Method and system for acoustic indoor positioning based on CDMA

Life of this patent

Abstract

Claims5