Research on Key Technology of Wireless Multimedia Communication for Mine
Rescue
Xue-zhao Zheng , Jun Deng, Yong-fei Jin
School of Energy Engineering,XI'an University of Scinence and Techmology, XI'an, China
(zhengxuezhao@yahoo.com.cn)
Abstract - The risk and complexity of the conditions and
environment in underground disaster area, restricted the use
and development of the mine rescue wireless multimedia
communications, and affected the rescue command and
decision to a certain extent. According to the needs of the site
this article discussed from the attenuation law of wireless
MESH networking signal in mine rescue process, the
synchronous acquisition and transmission technology of
multimedia information , the development technology of
intrinsically safe power supply and the reliability design of
the system devices , then inspected the actual effect of the
system devices through applications on site, and provided
reliable on-site information for experts and rescue command
staffs.
Keywords - Margins mine rescue, signal attenuation,
intrinsically safe power supply, and synchronous acquisition
I. INTRODUCTION
The environment and condition of coal-mining work
is usually complex and volatile in the places where the
extraordinarily serious disaster accident occurs suddenly,
especially in the process of dealing with the regional
calamity, thus the task of emergency rescue in mine is
relatively arduous, it is inevitable to overcome a series of
difficulties, including high temperature, dense smoke, gas
and excessive CO, insufficient light in coal mine, narrow
tunnel, unfavorable ventilation, etc. However, due to the
constraints of coal mine space as well as environment
condition, and meanwhile dragoman need to carry a large
number of first-aid and life saving equipments when they
go to the disaster area for emergency rescue in coal mine,
which will greatly consume the physical strength of
dragoman and affect the efficiency of rescue operation,
therefore it is extremely important to minimize the load
that dragoman has to carry and prepare the reliable and
communication apparatus with the greatest amount of
information. With the help of wireless communication
method, it is possible for dragoman to engage in the
rescue operation directly, thus the rescue procedures can
be simplified and the response speed of rescue can be
improved, dragoman can report the situation of disaster
area to underground rescue base and emergency rescue
command centers at different levels on the ground exactly
and effectively in real time, thus it can provide the
information in a more real-time and reliable manner for
command and decision-making in the process of rescue
and relief work to some extent. Therefore, it is necessary
to carry out the research on the characteristics, mechanism
of wireless multimedia communication data transmission
as well as the intrinsic safety and miniaturization of
equipments, and it is also urgent to develop the wireless
multimedia communication system which is appropriate
for the emergency rescue work in coal mine based on the
investigated theory, so as to transfer the information
during and after the process of rescue and relief work in
disaster area to underground rescue base and relief
headquarters on the ground as well as emergency rescue
command centers at different levels, it is of great
significance to enhance the ability of coal mine
emergency rescue and improve the national technology
level of rescue and relief work for mine accidents.
II. SYSTEM TECHNICAL PROPOSAL
It is a wireless multimedia communication system for
mine rescue which is convenient to carry when dragoman
provides disaster relief; this system adopts the
transmission plan of wireless MESH (mesh network)
networking; the equipment carried by dragoman in the
process of disaster relief is of compact size with reliable
performance, and it creates a system of its own with
various information, to support the real time transmission
of audio, video and environmental parameter data, and in
addition of that, it also has sufficient and reliable
bandwidth; it can be used to synchronously monitor a
variety of environmental parameters including
CH4(inflammable gas), O2(life support gas), CO and
T(temperature) for data acquisition, transmission and
storage; this system is equipped with a dynamic
topological structure, it is possible to acquire the gas
component in more than four directions by each node, all
nodes can work independently and they can be changed or
added whenever necessary, it is possible to increase the
number of acquisition points without restrictions by
adding more nodes; it has favorable transmission
performance and high quality of anti-interference; this
system has multiple methods for acquired data
presentation, which can be displayed on the ground and
underground synchronously, and moreover, it can provide
the interface for data output; it is equipped with the
function of alerting for rescue environment in case of any
abnormal environmental parameter.
I.
MAIN TECHNICAL PARAMETERS
(1) The transmission range of wireless function from
mine rescue base to disaster area ≥1000 meters,
accomplish the MESH networking more than 10 hops.
(2) Real time transmission of video, audio
information and environmental parameter;
(3) Base equipment and front-end equipment can
work independently as a separate system;
(4) Record the video and audio data information at
the site of accident in a real-time manner;
(5) Monitoring the images at the site of accident by
multiple points. 2 image presentation in the base, and 3
image presentation on the ground, talkback speech sounds;
(6) The weight of video and audio acquisition
equipment carried by draegerman≤2k.
(7) The wireless intrinsically safe type computer has
the function of commanding independently;
(8) Working time of system≥6h.
II. KEY TECHNOLOGY
A. Study on signal attenuation law of wireless MESH
networking in the process of mine rescue
Because the environment is complex and volatile in
mines, the space of tunnel is relatively narrow, there can
be coal and rock stratum all around in the tunnel, hackly
and irregular, there are also some supporting structures for
coal mining, electromechanical equipments as well as
steel rails and so on, thus it is a complex and non-free
space under the extremely special environment for
transmission, which can exert a significant influence on
the transmission characteristics of electromagnetic wave.
Especially in the mine hit by an adversity, its condition is
worse with complex landform, there will be turning
corners, branches and explosive gas within the tunnel, at
the meanwhile there is a large number of electromagnetic
interference in it, thus the communication environment is
extremely terrible. To solve these problems, this paper
carries out the research on the impact of various
conditions such as the section, gradient and roughness of
different tunnels on the transmission characteristics of
electromagnetic wave in wireless MESH networking
based on the previous studies. Moreover, a lot of
experiments have been conducted by utilizing the
simulated tunnel for mine safety production experiment in
Xian University of Science and Technology, and the
transmission characteristics of electromagnetic wave
within the waveguide have been taken as a reference in
the process of experiment research, Maxwell's equations
is used to work out the calculation results of wave mode
equation, to testify that the traditional research method of
metal waveguide theory can be applied in the research on
the transmission characteristics of electromagnetic wave
in tunnel in the process of wireless MSEH networking,
which can lay the foundation for studying about the
transmission characteristics in tunnels with specific
sections. Heavy graded tunnel with multiple turning
arched section and rectangular section is the basis for
actual research on tunnel. In the meantime, the wireless
radiofrequency is adjusted to test and verify that when the
operating frequency is in the high-frequency range, its
communication is table with strong flexibility, high signal
to noise ratio, high channel capacity, high speed of
information transmission, thus it is suitable for broadband
multimedia communication and convenient for
networking, the antenna and equipment for high
frequency is relatively small; in addition of this, the
electromagnetic interference for high frequency is less,
with wider transmission range and longer communication
span, which is exactly in favor of wireless multimedia
communication. However, the diffraction ability of
electromagnetic wave in the high-frequency range is weak,
and there are more demanding requirements for the
performance of receiving machine, and meanwhile, the
energy of electromagnetic wave is relatively stronger,
which conflicts with intrinsic safety, thus it needs to be
achieved by circuit control.
(1) After testing, the law curve between frequency and
horizontal polarization (aEh) as well as vertical
polarization (aEv) electromagnetic wave transmission
attenuation in the arched tunnel is shown in Fig.1 as
follows:
Fig.1 Attenuation law of electromagnetic wave in UHF frequency
range in the arched tunnel
(2) Impact of mine turning corners and branches on
wireless signal transmission
Due to the requirements of mining and ventilation,
the tunnels in mine are not straight, with turning corners
and branches. When the transmission frequency of
electromagnetic wave is constant, if the tunnel is more
winding, the transmission attenuation will be greater; at
the same turning, if the transmission frequency of
electromagnetic wave is higher, its attenuation will be
greater. At the same time, the branches in the tunnel will
intensify the transmission attenuation of electromagnetic
wave, the higher the transmission frequency of
electromagnetic wave is, and the greater the transmission
attenuation caused by branches will be.
Experimental data collected in the tunnels of Badin
Colliery mine of Shandong Yankuang Group is shown in
Fig.2 as follows. (From the experiment, it can be seen that
in the straight tunnel, the higher the frequency is, the
smaller the attenuation ratio will be, while in the winding
tunnel, the higher the frequency is, the greater the ratio of
attenuation will be, thus the trends of theoretical analysis
and test result are consistent.)
GHz of 240MIPS [3]. In the meanwhile, its embedded DSP
core has three ALUs with eight levels pipeline design,
which can support a variety of protocols, such as MPEG-4,
H.264／AVC, thus it can meet the demands of real time
system performance. The functional block diagram of
Hi3512 chip is shown in Fig. 3 as follows.
Fig.2 Attenuation law of wireless signal in straight tunnel and blinding
tunnel
(3) Application of MIMO-OFDM technology to solve the
interference and significant attenuation problem of
wireless communication signal in the process of mine
rescue
The resource of frequency spectrum is woefully
inadequate, which has become a bottleneck keeping down
the wireless multimedia communication and transmission
in mines with each passing day. Therefore, how to fully
develop and make use of the limited frequency spectrum
resource and improve the utilization rate of frequency
spectrum so as to minimize the information interruption
troubles caused by signal attenuation in the process of
mine rescue is one of the main research topics in this
paper. In this paper, it is designed that MIMO (MultipleInput Multiple-Output) technology and OFDM
(Orthogonal
Frequency
Division
Multiplexing)
technology are used to realize the data transmission at a
high speed in MESH networking and improve the quality
of transmission.
B. Study on synchronous acquisition and transmission of
multimedia data in the process of mine rescue
(1) Synchronous acquisition program with hardware
Hi3512 chip by HISILCON Company is selected as
the main hardware for synchronous acquisition of
multimedia data in mines, and it can achieve a series of
functions, including system control, H.264 video
compression and coding, audio signal processing, signal
transformation of environmental parameter, network
transmission, etc. The corresponding communication
interface of Hi3512 can be used to accomplish the initial
configuration work for video acquisition chip, audio
acquisition chip, data conversion chip, video coding and
compression chip. This chip adopts ARM926EJ—S and
DSP dual processor core as well as the so framework with
multiple cores and high integration density of hardware
acceleration engine, thus it has a strong ability of video
processing. In addition of that, it also has independent
16KB instruction Cache and 16KB data Cache, embedded
16KB instruction tightly coupled memorizer and 8KB
data tightly coupled memorizer, with DSP enhancement
structure, embedded 32×16MAC and Java hardware
accelerator, MMU is internally installed, thus it can
support various open operating system, with a maximum
Fig.3 Functional block diagram of Hi3512 chip
(2) Program with software
This software is a kind of dialog box structure
software, which is programmed by means of VC++
language under the integrated environment of Microsoft
Visual C++ 6.0 with the help of MFC and class library in
SDK provided by dual stream video server manufacturer,
and it run on the operating system platforms of Microsoft
such as Windows XP and Windows 7. The main
techniques in use contain graphical interface
programming technique, Socket network programming
technique, dynamic link technique, file operation
technique, custom message routing technique, etc. The
categories of dell Dynamic Link Library mainly include
network operation, audio and video coding-decoding
category, document literacy, synchronization and mutual
exclusion of critical resource. The specific function and
structure chart is shown in Fig. 4 as follows.
Fig.4 Structure chart of software for synchronous transmission of audiovideo and environmental parameter
① Software boot-up
Initialize the object which needs to be initialized in
OnInitDialog () function of main dialog box, mainly
including the appearance of software interface, setting for
some default initial values, as well as the software version,
etc.
② Network detection
Complete the initialization of Winsock by means of
WSAStartup (), that is the first step for Socket network
programming, so as to whether or not receive the
windows socket as well as the error number.
③ Equipment initialization and equipment detection
It is possible to acquire the network information of
network card for this computer by means of
gethostbyname (), so as to estimate whether this computer
and video server are within the same network or not, and
which network card to choose for communication. And
then, library function in SDK can be used to detect and
initialize the video server. HHNET_Startup () is used for
network
service
of
function
boot-up,
HHNET_SearchAllServer () function is applied to search
the digital video service equipment（DVS）in network,
HHNET_MessageCallback() sets the mechanism of
callback
function
for
message
handling,
HH5PLAYER_InitSDK()function
initializes
the
parameters
of
video
player,
HH5PLAYER_SetDecoderQulity () sets the quality of
video output, HH5PLAYER_InitPlayer2()can set the
video player window, HH5PLAYER_OpenStream() can
be used to start up the player to prepare for receiving the
video data which is sent back by video server and display
it by playing after decoding.
protection circuit constitutes of opened nanosecond triode
Q1 and field-effect tube Q2, the model number of triode
Q1 is 3906, while the model number of field-effect tube
Q2 is SI4435.The base of triode Q1 and the drain of fieldeffect tube Q2 are connected with the output end of
protection circuit respectively by electric resistance R3
and R4, the emitter of triode Q1 is connected with the
source of field-effect tube Q2; the collector of triode Q1 is
grounded by electric resistance R3 and R4, the grid
electrode of field-effect tube Q2 is connected between
electric resistance R3 and R4; capacitance C1 is in
parallel connection between the base and emitter of triode
Q1 for interference elimination. When the load works
normally, triode Q1 is in the status of cut-off, the fieldeffect tube Q2 is in the status of break-over, thus the
camera is in normal operation; once the camera breaks
down or any short circuit leads to the over current, the
potential of triode Q1 base is less than that of collector,
thus the triode Q1 will be in the status of break-over, the
voltage of field-effect tube Q2 is in the high level due to
the voltage division by electric resistance R4, the fieldeffect tube Q2 will be cut off within the time of
nanosecond, therefore the load can be protected
effectively.
C. Development technology for intrinsically safe power
source
Voltage output is 12V and 5V, and the capacity is
10Ah and 16Ah. There are no functions such as voltage
stabilization, over-current protection, over-voltage
protection, short circuit protection and the like in the
circuit, all the procedures of protection function are
doubly designed, so as to meet the demands of intrinsic
safety.
The key technology for intrinsically safe circuit lies
in cutting off quickly to protect the circuit. This overcurrent protection circuit by cutting off quickly consists of
opened nanosecond triode and closed nanosecond fieldeffect tube, and the base of opened nanosecond triode is
connected with the drain of closed nanosecond field-effect
tube by electric resistance, the emitter of opened
nanosecond triode is connected with the source electrode
of closed nanosecond field-effect tube, the grid electrode
of closed nanosecond field-effect tube is connected with
the divider resistance of collector circuit of opened
nanosecond triode. The above-mentioned triode plays a
role of monitoring the discharge current of power source,
if the voltage drop of this current on the triode and electric
resistance which is connected with the triode exceeds the
gate threshold voltage of this triode, this triode will be
opened within the time of nanosecond, the potential of
collector will become higher, which enable the fieldeffect tube is closed within the time of nanosecond, thus
the ignition energy of short circuit will be reduced in the
twinkling of an eye, to realize the purpose of eliminating
the hidden danger of explosion and protecting the load.
There is the circuit principle of an actual example of
new type over current protection circuit in Fig.5. This
Fig.5 Circuit principle diagram of intrinsically safe circuit
D. Design for system equipment reliability
Because the work environment and condition in coal
mine is complex and volatile, especially after the
accidental disaster happens, its environment will become
worse, thus the task of mine rescue is extremely arduous,
because it is necessary to overcome a series of difficulties
such as high temperature, dense smoke, gas and excessive
CO, insufficient light in coal mine, narrow tunnel,
unfavorable ventilation, etc. Therefore, it is required that
the equipment must be safe and reliable, to minimize the
rate of misoperation and improve the efficiency and safety
of rescue work. For this reason, it is necessary carry out
the redundancy design for equipment and make up
parallel system, so as to improve the reliability of
equipment. The reliability of equipment can be worked
out by means of formula (1).
r 1
R Hn   C ni (1  R ) i R ( n i )
i 0
Where
operation;
RHn
（1）
— Reliability of equipment in normal
C ni
— The number of events when i designs are in
normal operation among n safety designs;
R — Reliability of each safety design (it is supposed
that the reliability of each safety design will be the same).
For example, there are triple protections in the
process of designing the protection circuit, and the
specific parameters are as follows:
Over discharge cut-off delay: ≤0.10s
The first stage over current cut-off current: ＜2.60A
The second stage over current cut-off current: ＜1.30A
Over current cut-off delay: ≤105ns
Sort-circuit current: ＜15ma
Short circuit cut-off delay: ≤125ns.
III. APPLICATION OF SYSTEM EQUIPMENT
There is an event of gas explosion in a certain mine
in March of 2009, there is no casualty because the rescue
work is organized well, but the vertical drill holes 1# and
3# for gas drainage under suction are damaged, it is
unable to estimate the position of vertical drill hole
damage exactly no matter on the ground or in the mine,
which has brought much inconvenience for production
recovery in the mine, after the discussion made by the
expert group of accident investigation, the system
equipment is adopted to carry out the vertical drill hole
reconnaissance. Field force truss up the equipment with
mining intrinsically safe infrared video camera and miner
light, and they are put into the vertical drill holes 1# and
3# for gas drainage under suction by steel wire rope at a
low speed, respectively, the equipment records the
situation of vertical drill holes investigation in a ream
time manner when it is put down, and choke points are
detected at the 1#352m point and 3#353m point, which
provides the praiseworthy first hand information for
formulating the effective plan to repair the vertical drill
holes for gas drainage under suction; and the infrared
video camera also records the whole process of detection
instantaneously.
IV. CONCLUSION
This paper expounds and proves the existing
characteristics of various wireless communication systems
in mines based on the analysis on the environmental
features of coal mine after disaster, and it also puts
forward the technical data of wireless multimedia
communication for mine rescue, and in the meanwhile,
the following research on the key technology of system
equipment has been done.
(1) It studies the transmission characteristics of RF
electromagnetic wave in mines and makes the analysis on
the impact of environmental factors such as the sectional
area of tunnel, shape of section, turning corner, gradient,
support, branches and so on in the process of
electromagnetic wave transmission in the limited space,
and it is proposed in this paper that the design method of
MIMO-OFDM technique and MIMO technique can be
used to realize the high speed data transmission of MESH
networking and improve the quality of transmission.
(2) Based on the characteristics of mine emergency
rescue, it analyzes the synchronous acquisition method for
multimedia video-audio and environmental parameters in
the process of rescue work, Hi3512 chip is used for the
synchronous acquisition and encoding of video, audio and
environmental parameters. With the help of software
development tools such as Microsoft Visual C++ 6.0,
assorted SDK for dual stream network video server,
Microsoft Foundation Classes(MFC) and so on, it
develops the software system which has the functions of
searching and discovering the device address of server,
video monitoring by infrared video camera, video
recording, audio talkback transmission, sending control
signal, data acquisition and presentation by sensor,
warning as well as the synchronous acquisition of videoaudio and environmental parameters.
(3) It also carries out the design for intrinsically safe
portable power supply, and GB3836.4-2010 is taken as
the primary basis, to adopt IC main control chip for
battery protection, and based on the principle of minimum
ignition energy, the method for over current control and
short circuit cut-off time to control the spark ignition
energy, so as to meet the requirements of intrinsic safety.
(4) By means of field application, this paper also
makes efforts to test and verify that “wireless multimedia
communication system for mine rescue” can factually
describe the situation of field detection.
ACKNOWLEDGMENT
Foundation item: National Key Technology R&D
Program (2007BAK29B03), Natural Science Foundation
of China (51004081)
REFERENCES
[1] K. Akkaya, M. Younis, “A survey on routing protocols for
wireless sensor networks,” Ad Hoc Networks 2005, ch. 3,
pp. 325–349.
[2] G.E. Rolader, J. Rogers, J. Batteh, Self-healing minefield,
in: Proceedings of the SPIE – The International Society for
Optical Engineering, Battlespace Digitization and NetworkCentric Systems IV, 13–15 April 2004, vol. 5441, no. 1,
2004, pp. 13–24.
[3] K. Ikrath, W. Schneider, Communications via seismic
waves employing 80-Hz resonant seismic transducers,”
IEEE Transactions on Communications, 16 (3) (1968), pp.
439–444
[4] X. Jiang, J. Polastre, D. Culler, Perpetual environmentally
powered sensor networks, in: Fourth International
Symposium on Information Processing in Sensor Networks,
2005, pp. 463–468.
[5] J. Pan, B. Xue, Y. Inoue, A self-powered sensor module
using vibration-based energy generation for ubiquitous
systems, in: 6th International Conference on ASIC, vol. 1,
2005, pp. 443–446.