Wireless Communication Systems and Channel Characteristics 2
? 2002 by CRC Press LLC
2Satellite-Based Mobile
Communications
2.1 Introduction
A Brief History of Satellite Communications ?Types of
Telecommunications Satellite Services
2.2 Satellite Orbit Fundamentals
Orbital Mechanics ? Orbital Variations ? Types of Orbit ?
Orbit Selection
2.3 Satellite Radio Path
Path Loss in a Satelllite Link ?Frequency Selection
2.4 Multiple Access Schemes
2.5 Mobile Satellite Communications Systems
Geostationary Earth Orbit Mobile Satellite Services Systems ?Little-Low-Earth Orbit Systems ?Big-Low-Earth Orbit Mobile Satellite Services Systems 2.6 Summary
Mobile satellite communications began in 1976 with the launch by COMSAT of the MARISAT satellites to provide communications to ships at sea. The International Maritime Satellite Organisation (INMARSAT)was subsequently formed in 1979, and that organization now provides mobile satellite communications services to aircraft and land-based terminals. A number of national mobile satellite communications systems also serve the United States, Canada, Australia, and Japan with many more planned.
The spectacular growth of terrestrial mobile communications systems has provided a catalyst for efforts to provide global mobile communications through the use of mobile satellite communications systems in low-, medium-, and geostationary-Earth orbit.
Until now, second-generation terrestrial and satellite mobile communications systems have existed as two independent environments. However, these environments are beginning to combine to form a third-generation global mobile communications system in which terrestrial and satellite systems have comple-mentary instead of independent roles and form a single universal integrated system.
This chapter addresses satellite mobile communications systems, that is, satellite systems providing telecommunication services directly to mobile end users.
2.1.1 A Brief History of Satellite Communications
In an article in Wireless World in 1945, Arthur C. Clarke proposed the idea of placing satellites in geosta-tionary orbit around Earth such that three equally spaced satellites could provide worldwide coverage.However, it was not until 1957 that the Soviet Union launched the ?rst satellite Sputnik 1, which was followed in early 1958 by the U.S. Army’s Explorer 1. Both Sputnik and Explorer transmitted telemetry information.Michael John Ryan
University of New South Wales
The ?rst communications satellite, the Signal Communicating Orbit Repeater Experiment (SCORE), was launched in 1958 by the U.S. Air Force. SCORE was a delayed-repeater satellite, which received signals from Earth at 150 MHz and stored them on tape for later retransmission. A further experimental communication satellite, Echo 1, was launched on August 12, 1960 and placed into inclined orbit at about 1500 km above Earth. Echo 1 was an aluminized plastic balloon with a diameter of 30 m and a weight of 75.3 kg. Echo 1 successfully demonstrated the ?rst two-way voice communications by satellite.
On October 4, 1960, the U.S. Department of Defense launched Courier into an elliptical orbit between 956 and 1240 km, with a period of 107 min. Although Courier lasted only 17 days, it was used for real-time voice, data, and facsimile transmission. The satellite also had ?ve tape recorders onboard; four were used for delayed repetition of digital information, and the other for delayed repetition of analog messages. Direct-repeated satellite transmission began with the launch of Telstar I on July 10, 1962. Telstar I was an 87-cm, 80-kg sphere placed in low-Earth orbit between 960 and 6140 km, with an orbital period of 158 min. Telstar I was the ?rst satellite to be able to transmit and receive simultaneously and was used for experimental telephone, image, and television transmission. However, on February 21, 1963, Telstar I suffered damage caused by the newly discovered Van Allen belts. Telstar II was made more radiation resistant and was launched on May 7, 1963. Telstar II was a straight repeater with a 6.5-GHz uplink and a 4.1-GHz downlink. The satellite power ampli?er used a specially developed 2-W traveling wave tube. Along with its other capabilities, the broadband ampli?er was able to relay color TV transmissions. The ?rst successful trans-Atlantic transmission of video was accomplished with Telstar II, which also incor-porated radiation measurements and experiments that exposed semiconductor components to space radiation.
The ?rst satellites placed in geostationary orbit were the synchronous communication (SYNCOM) satellites launched by NASA in 1963. SYNCOM I failed on injection into orbit. However, SYNCOM II was successfully launched on July 26, 1964 and provided telephone, teletype, and facsimile transmission. SYNCOM III was launched on August 19, 1964 and transmitted TV pictures from the T okyo Olympics. The International Telecommunications by Satellite (INTELSAT) consortium was founded in July 1964 with the charter to design, construct, establish, and maintain the operation of a global commercial communications system on a nondiscriminatory basis. The INTELSAT network started with the launch on April 6, 1965, of INTELSAT I, also called Early Bird. On June 28, 1965, INTELSAT I began providing 240 commercial international telephone channels as well as TV transmission between the United States and Europe.
A second global satellite system was established by Intersputnik, founded in 1971, to serve the 14 socialist countries that had not joined the INTELSAT consortium. In 1979, INMARSAT established a third global system. In 1995, the INMARSAT name was changed to the International Mobile Satellite Organisation to re?ect the fact that the organization had evolved to become the only provider of global mobile satellite communications at sea, in the air, and on the land.
Early telecommunication satellites were mainly used for long-distance continental and intercontinental broadband, narrowband, and TV transmission. With the advent of broadband optical ?ber transmission, satellite services shifted focus to TV distribution, and to point-to-multipoint and very small aperture terminal (VSAT) applications. Satellite transmission is currently undergoing further signi?cant growth with the introduction of mobile satellite systems for personal communications and ?xed satellite systems for broadband data transmission.
2.1.2Types of Telecommunications Satellite Services
Because satellite communications cover the whole range of voice, data, and video transmission, telecom-munication satellite services are normally classi?ed into three types:
?Fixed satellite service (FSS) networks are mainly intended for long-distance operation of telecom-munications networks. FSS satellites are employed to relay signals between large, complex, and expensive Earth stations, which are connected to the terrestrial telecommunications network.
?Direct-broadcast satellite service (DBS) networks transmit broadcast and TV signals from a large central Earth station, via a satellite to receive-only Earth stations. DBS receive stations either are distribution heads for cable TV or are located in homes for direct-to-home transmission.
?Mobile satellite services (MSS) networks are relayed via satellite between large ?xed Earth stations and small mobile terminals ?tted to a ship, an aircraft, or a vehicle. Increasingly, MSS networks are formed to relay communications to portable handheld terminals.
In 1996, the ITU de?ned the Global Mobile Personal Communications by Satellite (GMPCS) as com-prising the following systems:
?Geostationary Earth Orbit (GEO) MSS are for voice and low-speed data mobile personal commu-nications services.
?Non-GEO (NGEO) MSS are for narrowband mobile personal communications services excluding voice — because these are invariably based on low-Earth orbit (LEO) satellites, they are also called Little-LEO.
?NGEO MSS for narrowband mobile personal communications include voice, operating in LEO, medium-Earth orbit (MEO), or highly elliptical orbit (HEO) — also called Big-LEO.
?GEO and NGEO FSS offer ?xed and transportable multimedia broadband services — also called Super-LEO.
This chapter focuses on MSS for personal communications and therefore considers the ?rst three of these systems: GEO MSS, Little-LEO MSS, and Big-LEO MSS.
2.2.1Orbital Mechanics
An understanding of how orbits are chosen and what limitations they have for satellite performance is important in the design and use of a satellite system. Although the ?eld of orbital mechanics is complex,
a limited understanding is suf?cient to consider the utility of various satellite orbits for MSS applications.
2.2.1.1Kepler’s Laws
Johann Kepler’s three laws apply to the motion of satellites in elliptical orbits. Kepler developed these laws empirically, based on conclusions drawn from the extensive observations of Mars by Tycho Brahe (taken around the year 1600). They were originally de?ned in terms of the motion of the planets about the sun, but apply equally to the motion of natural or arti?cial satellites about Earth.
First Law
Kepler’s ?rst law states that the satellite will follow an elliptical path in its orbit around the primary body, in this case Earth, which is at one of the foci of the ellipse. As illustrated in Fig. 2.1, the point at which the satellite is closest to Earth is called the perigee, and the point that it is farthest away is called the apogee. In many cases, the orbits selected for use by communications satellites are circular, which is the special case of an ellipse when both foci are coincident.
FIGURE 2.1Illustration of Kepler’s ?rst law.
Second Law
Kepler’s second law states that the line joining the satellite with the center of Earth sweeps out equal areas in equal times, as illustrated in Fig. 2.2. Area 1 is equal to area 2; the satellite sweeps out both areas in the same time. It follows that the satellite must move more quickly between points A and B than between points C and D.
Third Law
In his third law, Kepler stated that the cube of the mean distance of the satellite from Earth is proportional to the square of its period. Speci?cally, the orbit period of a satellite, T, at a height h above Earth’s surface is
where Earth’s radius R = 6,378,155 km, the gravitational constant G = 6.67 × 10–11 Nm 2/kg 2, and Earth’s mass M e = 5.95 × 1024 kg (neglecting the satellite mass).
2.2.2Orbital Variations
Kepler’s laws are suf?cient to study simple satellite motion, but are not accurate enough to describe real satellites whose orbits are perturbed by Earth’s gravitational anomalies and the effects of other bodies such as the sun and the moon. Earth is not a perfect sphere and the sun and the moon exert a gravitational pull on an orbiting satellite. These effects give rise to orbital perturbations and discrepancies between the motion predicted above and the actual motion of the satellite. Additionally, Earth’s orbit and rotation must be taken into account to orient the satellite’s orbit with respect to the stars.
2.2.2.1Oblateness and Equatorial Ellipticity
Kepler’s laws apply to bodies that are perfectly spherical. Earth is not a true sphere, with a ?attening at the poles, and the equatorial circumference not quite circular. The distance from the center of Earth to the north or south poles is less than at the equator by about 20 km. This oblateness of Earth, together with the fact that the equator is not a circle, means that the direction of the force of gravity acting on an orbiting satellite is not toward the center of Earth but is slightly displaced. These effects cause satellites to drift and adjustments are typically required every few months to return them to a nominally geosta-tionary position.
2.2.2.2Lunisolar Perturbations
Although the effects of the gravitational forces from the moon, and to a lesser extent the sun, are small compared with Earth, there are noticeable perturbations to a geostationary satellite through an inclination of the orbit to the equator. This is evident whether or not the orbit is initially inclined. The energy required to correct for lunar–solar perturbations (perform station-keeping ) is prohibitive for most satellite applications, although some satellites carry suf?cient fuel for such corrections. The more usual approach FIGURE 2.2
Illustration of Kepler’s second law.
for small geostationary satellites is to set the orbital inclination initially at 2° to 3°. The lunar–solar perturbation then causes the inclination to move through 0° and back to the initial angle in a period of 4 to 5 years, such that the angle of inclination remains small over the expected life of the satellite.
2.2.2.3Solar Radiation Pressure
For geostationary satellites, the effects of solar radiation pressure must also be considered. The effect increases with an increase in the size of the surface area of the satellite that is projected in the direction of the sun. This is the case for large powerful satellites that use large solar arrays. The net effect of the solar radiation pressure on a geostationary satellite is to increase the orbital eccentricity and to introduce a disturbing torque affecting the north–south axis of the satellite. Such perturbations are corrected periodically.
2.2.2.4Atmospheric Drag
Low-orbit satellites suffer atmospheric drag from the friction caused by collision with atoms and ions. The effect of drag is to reduce the ellipticity of an elliptical orbit, making it more circular, and to cause a loss of altitude of a circular orbit. At very low orbital altitudes the friction causes excessive heat on a satellite that ?nally results in its loss by burning. The orbital lifetime of a satellite (limited by drag) is a complex function of initial orbit height, geometry and mass of the satellite, and ionospheric conditions. However, in predicting a satellite’s life, the orbital life must be distinguished from the operational life. The latter is the period during which a satellite performs the planned mission successfully. Moreover, a satellite can continue to orbit for some time after ceasing to function. Conversely, a satellite on low orbit may well reach its orbital life well before its operational life would expire.
For example, the orbital life of a small satellite in a 400-km circular Earth orbit is typically a few months, whereas the orbital life of a similar satellite in an 800-km circular orbit could be several decades. In the case of the 400-km orbit, the functional life of the satellite is mainly governed by the orbital lifetime (except for the less likely situation where the satellite equipment fails earlier), whereas in the latter the functional life depends on the lifetime of the satellite equipment.
2.2.3Types of Orbit
The height of a satellite above Earth is a major factor in its utility for use within a communications system. Satellite height determines the orbit period, the time that the satellite is visible to a ground station, the footprint (coverage area on Earth’s surface), the propagation delay of signals to and from the satellite, and the path attenuation. Other physical in?uences include the two Van Allen radiation belts (Fig. 2.3);
FIGURE 2.3Satellite orbits and the Van Allen radiation belts.
peaks of radiation occur at altitudes of around 3,000 to 7,000 km and around 13,000 to 20,000 km where prolonged exposure can seriously shorten satellite lifetime. Additionally, altitudes lower than 400 km are uneconomical because of Earth’s gravity and the drag of the atmosphere that reduces satellite lifetimes. Four types of orbit are generally used for telecommunications satellites:
?Low-earth orbit (LEO) at heights of between 500 and 2,000 km
?Medium-earth orbit (MEO) between 5,000 and 15,000 km — also called intermediate circular orbit (ICO)
?Geostationary earth orbit (GEO) at 35,786 km
?Highly elliptical orbit (HEO) with an apogee that may be beyond GEO
2.2.
3.1Geostationary Earth Orbit
At geostationary altitudes, satellites have an orbital period equal to the period of rotation of Earth. Consequently, they remain in a ?xed position in respect to a given point on Earth. An obvious advantage is they are available to all Earth stations within their shadow 100% of the time. The shadow of a satellite includes all Earth stations that have a line-of-sight (LOS) path to it and lie within the radiation pattern of the satellite antenna. At geostationary altitude, the satellite has coverage of 17.3° cone angle, or about 40% of Earth’s surface. However, the polar areas are not covered.
Early launch vehicles did not have suf?cient capacity to lift useful payloads into geostationary orbit so lower orbits were employed. As launch vehicles improved, GEO satellites became the most popular for telecommunications satellites because they have the following advantages:
?Only three satellites are needed to provide global coverage.
?Each satellite has a large footprint.
?Each satellite remains stationary with respect to Earth, minimizing the need for the terminal to track the satellite.
?The transmitted signal has only a small Doppler shift (affecting synchronous digital systems) caused by satellite movement.
?The technology required is well known after almost 40 years of operating geostationary satellites. However, for mobile communications, GEO systems have the following major problems:
?High latency — round-trip delay of 250 ms leading to a total of 500 ms for a two-way conversation ?Poor coverage beyond 75° to 80° north and south of the equator
?High path attenuation (mostly from free-space loss) requiring high-power transmitters and large antennas at both the satellite and the mobile terminal
?Large losses resulting from shadowing by buildings in the urban environment
?Limited number of orbital slots available above each country
2.2.
3.2Low-Earth Orbit
LEOs have an altitude of 500 to 1000 km and move over Earth’s surface at velocities ranging from 6 to 8 km/s. In contrast to terrestrial mobile communications systems, LEO networks have a highly dynamic network topology. Handover occurs, not only because of movement of mobiles but also because of the satellites passing over the terminals. Because a single LEO cannot provide a communications link for more than a short period, constellations of LEOs are required to provide continuous coverage. The LEO concept was ?rst considered in the 1960s for transoceanic communications using passive re?ectors. However, cost and technological constraints restricted large-scale use of LEO systems until the 1990s, when interest in their use grew because of advances in technology coupled with the growing cost of placing GEO satellites into orbit, the congestion of the geostationary orbit, and the development of low-cost launchers.
Reasons why LEO systems are more suited to personal communications services include
?They can make use of small handheld terminals because they require less power and use small omnidirectional antennas.
?They can make more ef?cient reuse of frequencies.
?They have minimum propagation delay — even at a maximum LEO height of 1000 km, the latency is less than 3.3 ms for each uplink and downlink leading to a total of 13 ms for a two-way conversation.
?They are below the Van Allen belts.
?They are less subject to shadowing than GEO systems.
?They can provide communications coverage of the entire globe.
?They have low satellite launching costs because satellites can be injected directly into orbit, with the ability to launch several satellites in one launch.
However, the use of LEO systems does have some dif?culties, such as
?A large number of satellites are required to provide the same coverage as GEO systems.
?T o provide uninterrupted communications, frequent handover is required between satellites because of the speed at which the satellite is traveling across the ground.
?Satellites spend considerable time covering empty space (such as oceans and deserts).
?Satellites have a shorter lifetime because of orbital decay.
?Satellite lifetimes are also limited to 5 to 7.5 years because the satellite spends time in eclipse by Earth, providing a signi?cant demand on battery power.
2.2.
3.3Medium-Earth Orbit
MEO — also called intermediate circular orbits — orbit between 5,000 and 15,000 km above Earth’s surface. At those altitudes, a terminal would only see the satellite for slightly longer than 1 h, requiring approximately ten satellites in two planes (each plane inclined at 45° to the equator) for complete global coverage. MEOs have larger footprints than LEOs and require fewer satellites to provide the same coverage. However, they require larger, more capable payloads (larger antennas and higher power trans-mitters) to cater to increased transmission losses.
MEO systems are generally better suited to personal communications services than GEO and have the following advantages when compared with other orbits:
?They are between the Van Allen belts.
?Latency of 17 to 50 ms for each uplink and downlink leads to a total of 67 to 200 ms for a two-way conversation.
?Only a few satellites are required to cover the whole Earth, and each satellite has a relatively large footprint.
?Intersatellite handover is not as frequent as for LEO systems.
?Fewer eclipse cycles than LEO allow longer battery lifetimes of more than 7 years.
?Lower cosmic radiation leads to longer expected lifetimes.
?Higher average elevation angle from terminal to satellite reduces shadowing of LOS.
?Shorter slant ranges require less power than GEO systems, resulting in smaller satellites and mobile terminals.
However, the MEO systems also have some disadvantages, including
?Doppler frequency offsets are larger than for GEO because of higher relative satellite motion, but lower than for LEO.
?Although fewer satellites are required than for LEO, the trade-off between number of satellites and latency is generally considered suboptimum.
?Satellites spend considerable time covering empty space.
Satellite height (km)600–1,5009,000–11,00035,800
Orbital period (hr)1–26-824
Number of satellites40–808–202–4
Two-way propagation delay (ms)10–15150–250480–540
Satellite life (years)3–710-1510–15
Elevation angle Medium Best Good
Visibility of satellite Short Medium Permanent
Handheld terminal Possible Possible Restricted
Handover Frequent Infrequent None
Cost of satellite Maximum Minimum Medium
Gateway cost Highest Medium Lowest
Network complexity Complex Medium Simplest
Radio frequency output power Low Medium High
Propagation loss Low Medium High
2.2.
3.4Highly Elliptical Orbit
HEO satellites have an apogee that may be beyond GEO. Unlike GEO, HEO systems also cover the polar regions, which is why a HEO orbit was chosen for the Molniya system to provide coverage of the former Union of Soviet Socialist Republics. Molniya has a period of 12 h, 8 of which provides coverage of the operational region — for continuous coverage three satellites are required. HEO systems have the advantages of
?Coverage of the polar regions with a small number of satellites
?Lower launching costs
?Higher elevation angle for ground stations
?Lower atmospheric loss
However, HEO systems have signi?cant disadvantages such as
?Requirement for continual tracking of the satellite by Earth station
?Extensive eclipse periods
?Signal fading
?More complex control of the satellites and Earth stations
2.2.4Orbit Selection
The selection of orbit is effectively dictated by the speci?cations of the ground terminal. If the terminal is to be handheld, satellites need to be in LEO — or at least MEO — so that the terminal can use low powers and a small omnidirectional antenna. However, at these lower altitudes, the satellite footprint is signi?cantly reduced and a number of satellites are required depending on the altitude.
Table 2.1 summarizes the satellite systems as a function of orbit. Further design trade-off issues are discussed in later sections when speci?c systems are described.
In the radio path between the terminal and the satellite, the major attenuation tends to be caused by free-space loss. There is a multipath component, although this tends to be somewhat different from terrestrial paths. Doppler frequency shift is a signi?cant factor in all types of orbit, although it is most signi?cant in low-Earth orbits where the satellite has the highest speed across the ground. Propagation
between the satellite and the ground is also in?uenced by a number of factors that depend on the polarization of the wave.
2.3.1Path Loss in a Satelllite Link
2.3.1.1Free-Space Loss
The major loss in an Earth-satellite path is free-space loss, L FS , which is given by
where d s is the slant range in kilometers and f is in gigahertz.
Figure 2.4 shows the signi?cant increase in free-space loss as the altitude is increased from LEO to GEO altitudes (for a zenith path at 2 GHz).
2.3.1.2Atmospheric Absorption
Losses occur in Earth’s atmosphere as a result of energy absorbed by atmospheric gases. Absorption at any frequency is a function of temperature, pressure, humidity of the atmosphere, and elevation angle of the satellite. Absorption increases with frequency, as elevation angle is reduced and as propagation path is increased. Speci?c frequency bands have high absorption; the ?rst absorption band, caused by water vapor, is centered around 22.2 GHz, whereas the second band, caused by oxygen, is centered around 60 GHz.
2.3.1.3Ionospheric Effects
Radio waves traveling between satellites and Earth stations must pass through the ionosphere, which is the upper region of Earth’s atmosphere that has been ionized by solar radiation. The free electrons of this layer are not uniformly distributed but form layers. Furthermore, clouds of electrons (known as traveling ionospheric disturbances ) may travel through the ionosphere and give rise to ?uctuations in the signal that can only be determined on a statistical basis. The effects include scintillation , absorption ,variation in the d irection of arrival , propagation d elay , dispersion , frequency change , and polarization rotation . All these effects decrease as frequency increases, most in inverse proportion to the frequency squared, and only the polarization rotation and the scintillation effects are of major concern for satellite communications. Other effects are negligible at the frequencies of main interest for satellite communi-cation, except for a small fraction of time under events such as solar ?ares.
FIGURE 2.4Free-space loss vs. altitude for a zenith path for a 2-GHz signal.
L d f FS s =??()
924420.log
dB
Polarization Rotation
The radio path between the satellite and the ground is affected by a number of factors that depend on the polarization of the wave. Because the relative geometry of the path is time varying, linear polarization may be dif?cult to orient, particularly for handheld terminals that may be operated in random orientation.Additionally, the signal is subjected to varying degrees of Faraday rotation, particularly at low frequencies.Both these effects can be overcome by the use of circular polarization in personal communications systems. However, circular polarization is still sensitive to diffraction and re?ection of the signal resulting from obstacles in the path, because both re?ection and diffraction are polarization sensitive.Ionospheric Scintillation
Ionospheric scintillations are rapid variations in the amplitude, phase, polarization, or angle of arrival of radio waves. They are caused by small-scale refractive index variations in the F region of the ionosphere caused by local concentrations of ionization. The main effect of scintillations is fading of the signal. The fades can be quite severe, and they may last up to several minutes.
Ionospheric scintillation decreases in proportion to the inverse square of the frequency. Major scin-tillation is con?ned to frequencies below about 4 GHz. However, in extreme conditions such as magnetic storms, scintillation can cause problems up to 7 GHz.
Maximum levels of scintillation are observed in a region around the equator. Scintillation also increases in conditions of high solar activity and has a diurnal variation with high sunspot numbers; the peak levels occur approximately 1 to 2 h after sunset. It is interesting to note that, unlike tropospheric scintillation, ionospheric scintillation is independent of the elevation angle of the radio path.
When scintillation is expected at locations of interest, a link margin is provided to mitigate the effect.Link margins of several decibels could be required to achieve high link reliabilities for poorly sited Earth stations and operations below 3 to 4 GHz. At 4 GHz, attenuation resulting from ionospheric scintillation may vary from 0.5 to ~10 dB for 0.1% of the time, depending on the location and the level of solar activity.
2.3.1.4Attenuation from Hydrometers
Hydrometer is a general term referring to condensed water vapors in the atmosphere, which includes rain, hail, ice, fog, cloud, and snow. All types of hydrometers produce transmission impairments. How-ever, raindrops produce, by far, the maximum attenuation by absorbing and scattering radio waves.Rain attenuation is a function of rain rate (measured in millimeters per hour) in the region of an Earth station. The speci?c attenuation , α, can then be calculated:
where R p is the rain rate that would be exceeded p percentage time of the year, and a and b are coef?cients that depend on frequency and polarization.
Clouds and fog are suspended water droplets, usually less than 0.1 mm in diameter. Attenuation in the radio path depends on the liquid water content of the atmosphere along the propagation path. The liquid content of fog is generally low and the attenuation from fog is negligible for satellite communi-cations. Hail, ice, and snow have little effect on attenuation because of the low water content. However,ice can cause depolarization and subsequent polarization loss.
Only a small link margin is required below 2 GHz to accommodate the additional loss introduced by rainfall. However, at higher frequencies such as 20 to 30 GHz, the rainfall loss is very signi?cant, especially at low elevation angles where an additional link margin of tens of decibels may be required.
2.3.1.5Multipath Propagation
Unlike terrestrial communications, there are few multiple paths in the earth–satellite path. However,depending on the elevation of the satellite, the path can be obstructed by buildings and trees. From 0°to 20° elevation, the signal propagation is similar to that of terrestrial mobile communications systems in that it suffers frequent multipath effects and signi?cant blockage from obstacles. Above 20°, few α=()
?aR p b
dB km 1
multiple paths exist and the signal can generally be considered to be in free space. Unfortunately, most radio paths in personal communications are generally to LEO and MEO heights so that the typical maximum elevation of the satellite is not far above the lowest design elevation angle. The signals at the mobile terminal consist of a direct ray and a Rayleigh distribution of re?ected rays with various amplitudes and phases. The resulting distribution may be modeled by the Rice distribution.
Mitigation effects for multipath include the selection of coding and modulation techniques that are able to provide robust operation in a multipath fading environment. A common time-domain strategy is to use convolutional coding and interleaving. Alternatively, a frequency-domain approach is to use convolutional coding and a spread-spectrum technique. ARQ schemes are used to ensure that lost data is retransmitted. The use of high-gain antennas can also signi?cantly reduce multipath.
2.3.1.6Doppler Shift
The signal transmitted from the satellite is subject to a Doppler shift that results from motion of the satellite as well as the movement of the ground station because of the rotation of Earth. The received signal therefore has the frequency:
where f r is the received frequency, f d is the Doppler shift, and v r is the relative velocity of the satellite relative to the receiver. Note that the Doppler shift is affected by whether the satellite is approaching or receding, which results in the ambiguous ± sign.
2.3.2Frequency Selection
Table 2.2 lists the frequency bands allocated to satellite transmission. Commercial MSS systems predom-inantly operate in L-band, although systems will use C-band as well as Ka-band for satellite control and connection to gateways. As discussed earlier, lower frequencies experience lower attenuation. To minimize the power that must be generated onboard the satellite, the downlink frequency is chosen to be lower than the frequency for the uplink.
L-band is very useful for mobile communications because long wavelengths can penetrate many structures and less powerful transmitters are required. L-band is also the least affected by rain because rain attenuation is negligible in this band. However, L-band does suffer from ionospheric scintillation,which results in a split of the signal into direct and refracted paths. L-band also uses circular polarization to reduce the effect of Faraday rotation. S-band suffers less than L-band from ionospheric effects.However, it suffers slightly higher atmospheric attenuation from rain.
Ku-band has medium wavelengths that can penetrate many obstacles and provide high bandwidths.The band requires smaller antennas, but is more affected by rain attenuation.
Ka-band frequencies provide large amounts of available spectrum and high bandwidths. However,powerful transmitters are required and the short wavelengths are subject to strong rain fade — large rain attenuation creates a major technical challenge.L-band 1.6/1.5 GHz
Commercial Mobile S-band 3/2 GHz
Commercial Satellite control C-band 6/4 GHz
Commercial Fixed X-band 8/7 GHz
Military Fixed/mobile Ku-band 14/12 GHz
Commercial Fixed Ka-band 30/20 GHz
Commercial Fixed Ka-band
44/20 GHz Military
Fixed/mobile
Whenever access to a satellite is required for a number of Earth stations, it is necessary to employ a multiple-access scheme to allow for a distinct separation between the uplink and downlink transmissions to and from each Earth station. Three multiple access schemes are commonly used: frequency d ivision multiple accessing (FDMA), time division multiple accessing (TDMA), and code division multiple accessing (CDMA). Each scheme has its own characteristics, advantages, and disadvantages.
With FDMA, each Earth station is assigned speci?c uplink and downlink frequency bands within an allotted satellite channel bandwidth. That is, Earth station transmissions are separated in the frequency domain. Each terminal may operate independently with its own carrier, bandwidth, modulation, coding, and data rate. Antenna size varies for each terminal, based on individual link budget calculations. The disadvantages of FDMA include the requirement to reduce the transponder power by approximately one half to minimize intermodulation products. Precise control is also required over uplink power.
With TDMA, all Earth stations use the same carrier frequency and each station transmits a short burst of information during a speci?c time slot (epoch) within a TDMA frame. The bursts must be synchro-nized so that each station’s burst arrives at the satellite at a different time. That is, transmissions from different Earth stations are separated in the time domain. TDMA is generally superior to FDMA because intermodulation distortion is lower and the full downlink power is available to all users. The main disadvantage is the requirement of accurate timing and synchronization.
With CDMA (sometimes called spread-spectrum multiple access), all Earth stations transmit within the same frequency band and, for all practical purposes, have no limitation on when they may transmit. Signal separation is accomplished by spread-spectrum techniques where each user has a unique code that is used to generate a pseudorandom sequence that is used to spread out the transmission to occupy the entire bandwidth. That is, users are separated by a unique code. At the receiver, the spread signal is despread by applying the same code to the received data. Although CDMA provides high immunity to jamming and has a low probability of interception, it is expensive and can cater to only a limited number of users.
As discussed earlier, the ITU GMPCS de?nes three systems for the provision of MSS for personal communications as follows:
?GEO MSS — satellites operating in geostationary orbit providing voice and low-speed data mobile personal communications services
?Little-LEO — NGEO MSS for narrowband mobile personal communications services excluding voice, generally operating in LEO
?Big-LEO — NGEO MSS for narrowband mobile personal communications including voice, oper-ating in LEO, MEO, or HEO
The next section brie?y describes the major MSS systems for personal communications.
2.5.1Geostationary Earth Orbit Mobile Satellite Services Systems
This section brie?y gives a short outline of major GEO MSS systems, which use satellites in geostationary orbit to provide voice and low-speed data mobile personal communications.
INMARSAT was created in 1979 with approximately 40 members and has grown to more than 81 member countries. In 1990, INMARSAT launched four satellites into geostationary orbit and launched a ?fth satellite in 1998. The new satellites are capable of providing spot beams to increase capacity by more than 20 times over earlier generations. The main advantage is that the increased power and sensitivity of the newer satellites has allowed a signi?cant reduction in the size of the earth terminals, which are now little bigger than a laptop computer. Although INMARSAT provides a number of services,
the most mobile is the INMARSAT-M terminal, which is briefcase sized and can provide global digital 6.8-kbps voice and 2.4-kbps fax and data.
Agrani is Afro-Asian Satellite Communications (ASC). Agrani is expected to cover 54 countries —Turkey to Singapore and Byelorussia to Somalia including the Middle East, India, and much of China. Two GEO satellites provide mainly voice, but also provide fax, data, and messaging for ?xed and mobile users. The ?rst satellite (expected in 2002) will mainly cover the Indian region, with the second extending coverage across Africa.
The American Mobile Satellite Corporation (AMSC) satellite provides coverage of the United States and regions of U.S. coastal waters, providing voice, messaging, and data services.
The Asian Cellular Satellite System (ACes) Garuda-1 satellite was successfully launched in February 2000. ACes covers most of Asia from Pakistan to Japan, including southern China and all Association of Southeast Asian Nation (ASEAN) countries and provides mobile and ?xed voice, data, fax, and paging. Euro-African Satellite Telecommunications (EAST) is planned to provide a range of services including narrowband communications to handheld user terminals and higher bandwidth services to VSAT anten-nas. Optus MobileSat II comprises the Australian Optus B1 and B3 satellites and ground stations in Perth and Sydney. Over 1500 mobile terminals operate in the D-band with uplinks and downlinks at 1.6 and 1.5 GHz, respectively. These enable users to communicate from any location on the Australian mainland and 200 km out to sea. Both voice and low-rate data communications are provided.
Thuraya plans to provide high-powered GEO satellites that will cover a footprint of 99 countries throughout Europe, North and Central Africa, the Middle East, Central Asia, and the Indian Subconti-nent. The ?rst satellite was launched in October 2000. Thuraya will provide voice, fax, data, messaging, and global positioning system (GPS) within handheld and vehicular telephones that will integrate both satellite and cellular communications. A second satellite is planned to provide backup and expansion; a third satellite may follow if required. Other planned GEO MSS systems include: Africom, APMT, and Cyprus GEM.
2.5.2Little-Low-Earth Orbit Systems
Little-LEO systems are non-GEO (NGO) MSS for narrowband mobile personal communications services excluding voice. Advances in antenna design, signal reception, and miniaturization have allowed the deployment of small LEO systems that can support data transmission at 100 to 300 bps. These systems operate at a frequency below 1 GHz and are only appropriate for nonvoice, store-and-forward messaging.
2.5.2.1OrbComm
OrbComm was granted a license by the U.S. Federal Communications Commission (FCC) in 1994 and the ?rst two satellites were launched in April 1995. OrbComm provides mobile tracking, remote moni-toring, and commercial and personal messaging services. The ?nal OrbComm constellation will consist of 48 small (40 kg) satellites in LEO with a planned life of approximately 4 years. Space-to-ground communications is via very high frequency (VHF): 148 to 150.05 MHz uplink and 137 to 138 MHz downlink. Terminals will transmit at a burst rate of 2.4 kbps and receive at a burst rate of 4.8 kbps giving an effective throughput of 300 bps.
Messages will be sent via OrbComm satellites to gateway stations on Earth, which will either forward the message directly to the destination via terrestrial networks, or store it for access on demand. Although the effective throughput is low, global coverage is provided.
2.5.2.2Other Systems
VITAsat is managed by Volunteers in Technical Assistance (VITA), a U.S. nonpro?t organization dedicated to bringing technical assistance to the developing world. It has entered into agreements permitting usage of two already-orbiting satellites (HealthSat-2 and UoSAT-12) to bring low-cost e-mail services to rural and isolated areas of developing countries.
Leo One Worldwide has announced a little-LEO data-messaging system based on 48 satellites at 950 km in eight orbital planes inclined at 50°. The system will provide data rates of 2.4 to 9.6 kbps for the
subscriber uplink and 2.4 kbps for the subscriber downlink. Gateway uplinks and downlinks will operate at 50 kbps. Other systems proposed include E-Sat, and GEMnet.
2.5.3Big-Low-Earth Orbit Mobile Satellite Services Systems
Big-LEO systems are NGEO MSS for narrowband mobile personal communications including voice, operating in LEO, MEO, or HEO. These systems operate between 1 and 3 GHz and provide the full range of mobile services including voice and data. They are generally more complex than little LEOs and more satellites are deployed.
2.5.
3.1Iridium
The ?rst fully functioning big-LEO system was Motorola’s Iridium, which was probably the most complex of the MSS personal communications systems, providing worldwide voice, data, facsimile, and paging. Iridium satellites perform onboard processing, not only to translate a waveform frequency and retransmit it, but also to process the waveform down to baseband. This allows the satellites to support a variety of packet-oriented services, including routing, ?ow control, and error detection and correction.
The Iridium space segment consists of 72 satellites arranged in six orbital planes with 11 active and 1 spare satellite per plane at an altitude of 780 km. Satellites were expected to have a life of 5 to 7 years. Each satellite had 48 spot beams, each of which could be shared four ways using time division — the L-band, TDMA-TDD system provided 230 simultaneous conversations per satellite.
Iridium is the only big LEO to use intersatellite links to obviate the need to downlink traf?c to hub stations on Earth. Each satellite has four cross-links; one forward within a plane, one backward within a plane, and two across planes. Cross-links operate at 25 Mbps at frequencies between 22.55 and 23.55 GHz. Although onboard processing and satellite cross-links increase ?exibility, the advantages are offset by an increase in complexity and satellite weight (500 kg) leading to a satellite cost of U.S. $62 million. Iridium phone calls are made through the shortest route including the satellite constellation to the terrestrial gateway closest to the destination. Intersatellite links and onboard satellite switching are used to route calls back to a satellite that can “see” a ground terminal. To provide global coverage, 12 ground stations are employed.
Despite meeting most planning deadlines, Iridium failed to attract suf?cient subscribers to avoid bankruptcy and, in March 2000, the service was closed. Plans to bring the constellation of satellites down in a controlled reentry were aborted in late 2000 when the assets of Iridium LLC were acquired by Iridium Satellite LLC. The new owner does not see Iridium as a mass consumer service and intends to concentrate on industrial markets and specialized segments.
2.5.
3.2Globalstar
Globalstar has adopted a much simpler approach than Iridium and has employed satellites as a bent pipe with the same technology as used in GEO-based systems. The Globalstar system has 48 satellites twice as high as Iridium at an altitude of 1414 km inclined at 45° and 135° to the equator. Satellites have a lifetime of 5 to 15 years, weigh 704 lb, and have a capacity of 2800 full-duplex circuits. The constellation has eight orbital planes and covers from 70° south to 70° north. Globalstar signals go up to the nearest satellite and down from there to a terrestrial gateway that the satellite can see and are then passed on to existing ?xed and cellular telephone networks; the satellite must be in sight of a ground station to complete a call. Complex intersatellite routing is avoided by having 38 ground stations worldwide.
Globalstar offers voice, SMS, roaming, positioning, facsimile, and data. Satellites have six spot beams using L-band CDMA; the full constellation can provide 28,000 simultaneous voice and data channels at 4.8 kbps.
2.5.
3.3Ellipso
Ellipso provides UHF CDMA voice, messaging, and positioning services through 17 satellites. Two inclined, elliptical orbital planes (with an apogee of 2903 km and a perigee of 425 km), each with ?ve satellites effectively providing a LEO system in the Southern Hemisphere and a MEO system in the
Northern Hemisphere. Ellipso will also launch seven of its satellites into two slightly inclined circular planes around the equator to supplement services in the tropics.
The Ellipso ground segment employs 12 ground control stations (GCSs), deploying them near regional ?ber hubs for networking ef?ciency. Each GCS typically tracks and uses two satellites while acquiring a third. The GCS also determines the position of subscriber terminals for administrative, billing, and application purposes.
2.5.
3.4Intermediate Circular Orbit
The Intermediate Circular Orbit (ICO) system was developed as a spin-off from INMARSAT (originally called INMARSAT-P, or Project 21). ICO provides full Earth coverage with ten satellites at 10,355 km arranged in two planes of ?ve satellites in each plane. Satellites have an orbital period of 6 h with each satellite being visible from one point on Earth’s surface for typically about 20 min. Twelve ground stations, called satellite access nodes (SANs), are linked by high-speed terrestrial networks. ICO terminals are dual-mode (satellite and terrestrial) handsets and all operations are through existing cellular networks. ICO signals go from ground station to satellite to ground station with users at each end connecting through cellular and land networks. Each ICO satellite has a capacity of around 4500 voice channels using S-band CDMA.
The original ICO system suffered a number of early problems including launch failures during which one satellite was lost. ICO has emerged from bankruptcy with investment from ICO-T eledesic. NewICO has a planned service start date of 2003.
2.5.
3.5Constellation ECCO
The Constellation ECCO system will consist initially of one plane of 12 satellites (11 operational and 1 spare) in circular orbit around the equator, at an altitude of 2000 km. The satellites will transmit directly to mobile and ?xed-site users in the 2483.5 to 2500 MHz band and receive directly from these users in the 1610 to 1626.5 MHz band. The system will provide phone and data services to all areas between the tropics. Each satellite will have 24 antenna beams that collectively cover one eleventh of the equatorial belt. Each of the ?rst-generation satellites will be able to support up to 192,000 subscribers and the whole system will be able to support as many as 1,392,000 subscribers. The design lifetime of these satellites is
a minimum of 5 to 7 years.
2.5.
3.6Other Systems
Other planned big-LEO systems include Movisat, MSAT, and Satphone.
Over the next few years, a large number of consortia have launched, or are preparing to launch, constel-lations of satellites that will provide continuous, global phone and data services to mobile terminals. Most systems will be launched into LEO where there are considerable advantages to be gained over higher orbits. Because of the lower altitude, mobile terminals can be small personal handsets with low antenna gain and low-output power. These systems hold the promise of achieving third-generation mobile communications systems of integrating terrestrial and satellite networks providing a similar interface to a small handheld terminal.
References
Comparetto, G., and Ramirez, R., Trends in mobile satellite technology, IEEE Computer, 44, 1997. Elbert, B.R., The Satellite Communications Application Handbook, Artech House, Norwood MA, 1997. Evans, J.V., Satellite systems for personal communications, IEEE Antennas and Propagation Magazine, 39, 1997.
Jamalipour, A., Low Earth Orbital Satellites for Personal Communication Networks, Artech House, Nor-wood MA, 1998.
Kiesling, J.D., Land mobile satellite systems, Proceedings of the IEEE, 78, 1107, 1990.
Miller B., Satellites free the mobile phone, IEEE Spectrum, 26, 1998.
Ohmori, S., Wakana, H., and Kawase, S., Mobile Satellite Communications, Artech House, Norwood MA, 1998.
Pattan, B., Satellite-Based Global Cellular Communications, McGraw-Hill, New Y ork, 1998.
Silk, R., and Bath, M., Future trends in satellite communications, British Telecommunications Engineering, 17, 73, 1998.
Wu, W.W., Miller, E.F., Pritchard, W.L., and Pickholtz, R.L., Mobile satellite communications, Proceedings of the IEEE, 9, 1994.
4G无线通讯系统简介
KT319矿用无线通信系统 4G矿用无线视频和通讯系统解决方案 北京唐柏通讯技术有限公司 二○一四年一月
1.矿用无线通讯系统发展现状 通信系统作为煤矿六大系统的重要组成部分在现代化大中型矿山企业中正扮演着越来越重要的角色。传统的有线通信系统具有语音通话、电话调度、会议汇接等基本功能，广泛应用于井下生产指挥与人员通信联络。 随着技术水平的提高，通信和调度功能包含了更多内容。通信除了语音电话之外，还增加了文本、多媒体视频、传感器采集与控制等信息的传递。调度也不仅限于固定电话调度，加入了移动终端调度和多媒体的元素，并可与人员定位、应急广播等其它系统整合联动，使得生产调度与应急指挥更加直观、准确、快捷。由此，对通信系统采用的技术提出了更高要求：一方面传统的有线通信（固话）向有线、无线融合通信（固话+移动终端）升级已成为大势所趋；另一方面，在基于IP分组交换的宽带通信网络之上应该可以叠加更丰富的数字业务，适应信息化建设对传输承载的需求。 针对PHS无线系统、WiFi无线系统，3G无线系统，4G无线系统等三,种类型矿用无线通信系统及其在煤矿中的使用情况作对比，由此提出最优技术方案。 PHS无线系统 PHS(小灵通)无线市话技术源自日本，是固定电话的有效延伸和补充，被称为“固话的补充和发展”。PHS系统在煤矿井下实际使用，存在着功能单一，无数据传输能力，信号传输距离短、基站非本安型等问题。且目前小灵通将要彻底退网，所有生产厂家都已停止生产，设备及板件无法买到，对现役系统今后的维护及故障处理造成很大困难。 WiFi无线系统 WiFi无线通信系统目前在煤矿应用很多，有着带宽高、连接稳定的优点。WiFi非常适合用来为无线高清摄像机、无线开关等移动性要求不高，带宽需求较高，需要长时间保持数据连接的设备提供接入通道。若用来作为人员通信则存在一些难以解决的问题：（1）WiFi信号穿透能力差，极易受障碍物阻挡和干扰，复杂环境下数据传输不稳定，通话音质无保证； （2）WiFi基站在井下实际覆盖距离较近，一般直线只有不到300米，加上2.4GHz信号拐弯能力差，因此需要布设较多的基站才能实现全覆盖； （3）WiFi系统对终端在基站间切换支持不好，通话中终端发生切换容易因丢包导致掉话；
无线传感器网络试题库1教学内容
无线传感器网络试题 库1
《无线传感器网络》 一、填空题（每题4分，共计60分） 1.传感器网络的三个基本要素：传感器、感知对象、用户(观察者) 2.传感器网络的基本功能：协作式的感知、数据采集、数据处理、发布感知 信息 3、 3.无线传感器节点的基本功能：采集数据、数据处理、控制、通信 4.无线通信物理层的主要技术包括：介质选择、频段选取、调制技术、扩频 技术 5.扩频技术按照工作方式的不同，可以分为以下四种：直接序列扩频、跳 频、跳时、宽带线性调频扩频 6.定向扩散路由机制可以分为三个阶段：兴趣扩展阶段、梯度建立阶段、路 径加强阶段 7.无线传感器网络特点：大规模网络、自组织网络、可靠的网络、以数据为 中心的网络、应用相关的网络 8.无线传感器网络的关键技术主要包括：网络拓扑控制、网络协议、时间同 步、定位技术、数据融合及管理、网络安全、应用层技术 9.IEEE 802.15.4标准主要包括：物理层。介质访问控制层 10.简述无线传感器网络后台管理软件结构与组成：后台管理软件通常由数据 库、数据处理引擎、图形用户界面和后台组件四个部分组成。 11.数据融合的内容主要包括：多传感器的目标探测、数据关联、跟踪与识 别、情况评估和预测 12.无线传感器网络可以选择的频段有：_800MHz___915M__、2.4GHz、___5GHz
13.传感器网络的电源节能方法：_休眠（技术）机制、__数据融合 14.传感器网络的安全问题：(1) 机密性问题。 (2) 点到点的消息认证问题。 (3) 完整性鉴别问题。 15.802.11规定三种帧间间隔：短帧间间隔SIFS，长度为 28 s a)、点协调功能帧间间隔PIFS长度是 SIFS 加一个时隙(slot)长度，即 78 s b)分布协调功能帧间间隔DIFS ，DIFS长度=PIFS +1个时隙长度，DIFS 的长度为 128 s 16.任意相邻区域使用无频率交叉的频道是，如：1、6、11频道。 17.802.11网络的基本元素SSID标示了一个无线服务，这个服务的内容包括 了：接入速率、工作信道、认证加密方法、网络访问权限等 18.传感器是将外界信号转换为电信号的装置，传感器一般由敏感元件、转换 元件、转换电路三部分组成 19.传感器节点由传感器模块、处理器模块、无线通信模块和能量供应模块四 部分组成 20.物联网是在计算机互联网的基础上，利用RFID、无线数据通信等技术，构 造一个覆盖万物的网络。RIFD无线识别、嵌入式系统技术、能量供给模块和纳米技术列为物联网关键技术。 二、基本概念解释（每题5分，共40分） 1.简述无线网络介质访问控制方法CSMA/CA的工作原理 CSMA/CA机制:
安防监控系统建设施工技术方案
安防监控系统建设施工技术方案 一、方案概述 随着现代化企业制度在我国的普及和深化发展，企业的信息化建设不断深入，各企业特别是大中型企业都加快了信息网络平台的建设；企业正逐步转向利用网络和计算机集中处理管理、生产、销售、物流、售后服务等重要环节的大量数据。 为了更好的保护财产及酒店的安全, 根据企业用户实际的监控需要，在酒店的大厅，楼道，过道，机房，停车场等重点部位安装摄像机。监控系统将视频图像监控,实时监视,多种画面分割,多画面分割显示,云台镜头控制,打印等功能有机结合的新一代监控系统，同时监控主机自动将报警画面纪录,做到及时处理,提高了保卫人员的工作效率并能及时处理警情，能有效的保护酒店的财产和工作人员的安全,最大程度的防范各种入侵,提高处理各种突发事件的反映速度,给顾客提 供一个良好的环境,确保整个酒店的安全。 酒店工作人员利用桌面微机，随时了解各主要区域的安全状况，处理突发事件，酒店闭路监控系统实施可实现其功能为： 1 实时对大门，楼道进行高清晰视频监控 2 可录制各点的视频录像以备安防查用 3 有效保证前台人员的安全规范操作 4 调节镜头的焦距可以清晰的观测到客人出入的具体细节 为进一步满足社会经济发展与人们文明生活的高标准要求，创造一个安全、舒适、温馨、高效的住宿环境，根据酒店实际情况，酒店监控分为室内监控和室外监控两部分，室内为酒店内部的监控，夜晚有灯光光线较好，使用普通摄相机即可，室外部分夜晚无路灯，采用红外摄相机以提高监控效果。 二、设计原则 本项目方案设计遵循技术先进、功能齐全、性能稳定、节约成本的原则。并综合考虑施工、维护及操作因素，并将为今后的发展、扩建、改造等因素留有扩充的余地。本系统设计内容是系统的、完整的、全面的；设计方案具有科学性、合理性、可操作性。其具有以下原则： 1、先进性与适用性 系统的技术性能和质量指标应达到国际领先水平；同时，系统的安装调试、软件编程和操作使用又应简便易行，容易掌握，适合中国国情和本项目的特点。该系统集国际上众多先进技术于一身，体现了当前计算机控制技术与计算机网络技术的最新发展水平，适应时代发展的要求。同时系统是面向各种管理层次使用的系统，其功能的配置以能给用户提供舒适、安全、方便、快捷为准则，其操作应简便易学。 2、经济性与实用性 充分考虑用户实际需要和信息技术发展趋势，根据用户现场环境，设计选用功能和适合现场情况、符合用户要求的系统配置方案，通过严密、有机的组合，实现最佳的性能价格比，以便节约工程投资，同时保证系统功能实施的需求，经济实用。 3、可靠性与安全性
无线传感器网络技术试题
无线传感器网络技术试 题 Company Document number：WTUT-WT88Y-W8BBGB-BWYTT-19998
一、填空题 1. 传感器网络的三个基本要素：传感器、感知对象、用户(观察者) 2. 传感器网络的基本功能：协作式的感知、数据采集、数据处理、发布感知信息 3. 无线传感器节点的基本功能：采集数据、数据处理、控制、通信 4. 传感节点中处理部件用于协调节点各个部分的工作的部件。 5. 基站节点不属于传感器节点的组成部分 6. 定向扩散路由机制可以分为三个阶段：兴趣扩展阶段、梯度建立阶段、路径加强阶段 7. 无线传感器网络特点：大规模网络、自组织网络、可靠的网络、以数据为中心的网络、应用相关的网络 8. NTP时间同步协议不是传感器网络的的时间同步机制。 物理层。介质访问控制层 10. 从用户的角度看，汇聚节点被称为网关节点。 11. 数据融合的内容主要包括：多传感器的目标探测、数据关联、跟踪与识别、情况评估和预测 13. 传感器网络的电源节能方法：_休眠（技术）机制、__数据融合 14. 分布式系统协同工作的基础是时间同步机制 15. 无线网络可以被分为有基础设施的网络与没有基础设施的网络，在无线传感器网络，Internet网络，WLan网络，拨号网络中，无线传感器网络属于没有基础设施的网络。 16. 传感器网络中，MAC层与物理层采用的是IEEE制定的IEEE协议
17. 分级结构的传感器网络可以解决平面结构的拥塞问题 18. 以数据为中心特点是传感器网络的组网特点，但不是Ad-Hoc的组网特点 19. 为了确保目标节点在发送ACK过程中不与其它节点发生冲突，目标节点使用了SIFS帧间间隔 20. 典型的基于竞争的MAC协议为CSMA 二、选择题 1.无线传感器网络的组成模块分为：通信模块、（）、计算模块、存储模块和电源模块。A A．传感模块模块 C网络模块 D实验模块 2..在开阔空间无线信号的发散形状成（）。A A．球状 B网络 C直线 D射线 3.当前传感器网络应用最广的两种通信协议是（）D A. B. C. D. 4.ZigBee主要界定了网络、安全和应用框架层，通常它的网络层支持三种拓扑结构，下列哪种不是。D A．星型结构、B网状结构C簇树型结构D树形结构 5.下面不是传感器网络的支撑技术的技术。B A．定位技术B节能管理C时间同步D数据融合 6.下面不是无线传感器网络的路由协议具有的特点D A．能量优先 B.基于局部拓扑信息 C.以数据为中心 D预算相关 7.下面不是限制传感器网络有的条件C A电源能量有限 B通信能力受限 C环境受限 D计算和存储能力受限
KT160矿用无线通信系统说明
KT160矿用无线通信系统说明一、系统结构 系统可分为两种结构，光纤独立组网和工业以太环网组网。 光纤独立组网： 工业以太环网组网：
二、系统功能 1、基本功能 语音调度功能完整和丰富的新业务能力扩展 1.1 通话 系统具有对所注册的号码进行拨打，接通后进行语音通话的功能。 系统具有接听注册用户对总台的电话，并进行通话的功能。 1.2 群呼 同时呼叫某一个群中的所有分机。 1.3 组呼 对选中的某些分机发起呼叫。 1.4 呼叫记录显示 显示服务器所有的分机通话记录。 1.5 转接 控制台将总机接通的通话转移给某一个分机。 1.6 代接 控制台总机接听正在振铃的一路通话。 1.7 强插 控制台插入已经开始的通话，实现总机与通话双方的多方通话。 1.8 强拆 控制台强行中断某一通话。 1.9 监听 控制台总机监听某一个通话。 ? 呼叫 ? 强插 ? 强拆 ? 监听 ? 选呼 ? 群呼 ? 热线呼叫 ? 呼叫前转 ? 遇忙转移 ? 个人跟随 ? 定时叫醒 ? 缩位拨号 ? 选择应答 ? 呼叫等待 ? 呼叫代接 ? 会议电话 ? 呼出限制 ? 呼入限制 ? 紧急呼叫 ? 呼叫锁定 ? 手动录音 ? 自动录音 ? 组内限制 ? 级别限制
1.10 加入会议 控制台邀请分机到指定会议室。 1.11 邀请外线 邀请用户输入的外线号码到会议室中。 1.12 存储和查询 系统具有对所有通话的存储和查询功能： 1.13 显示 系统具有列表显示功能： a) 对所有分机的列表显示； b) 对所有在线分机的的列表显示； c）对所有通话中的分机列表显示； d）对各个组内分机的列表显示。 1.14 打印 系统对通话记录、注册用户明细等报表的打印功能。 1.15 人机对话 系统具有人机对话功能，以便于系统生成、参数修改、功能调用、控制命令输入等。 1.16 自诊断 系统具有自诊断功能。当手机不再服务区，系统将显示该手机处于离线状态，如果在服务区，将显示在线状态。 1.17 备用电源 系统具有备用电源。当电网停电后，保证整个系统的正常运行。 1.18 数据备份 系统具有数据备份功能，可以定时对服务器中的数据进行备份。 1.19 防雷 系统中在井下和机房之间采用光缆连接。 中心站设备的电源输入口接入OVR40型电源避雷器。 1.20 其他 系统具有网络通信功能。 系统具有软件自监视功能。 系统具有软件容错功能。
(完整版)无线传感器试题库
无线传感器网络试题 一填空题 1、传感器是一种检测装置，能感受到被测量的信息，并能将检测感受到的信息，按一定规律变换成为电信号或其他所需形式的信息输出，以满足信息的传输、处理、存储、显示、记录和控制等要求。 2、感知目标、网络节点、用户构成了无线传感器网络的三个要素。 3、无线传感器网络的通信协议栈包括物理层、数据链路层、网络层、传输层和应用层与互联网协议栈的五层协议相对应 4、无线传感器网络的产业化障碍包括四个方面。它们分别是：大规模组网问题、大规模组网问题实用化低功耗技术、微型化加剧信号串扰、可靠性提高资源需求 二、判断题 1、无线通信是利用电磁波信号可以在自由空间中传播的特性进行信息交换的一种通信方式（对） 2、SINK节点：亦称网关节点，与簇头结点的功能完全相同。（错） 3、通过拓扑控制自动生成的良好的网络拓扑结构，能够提高路由协议和MAC协议的效率，可为数据融合、时间同步和目标定位等很多方面奠定基础，有利于节省节点的能量来延长网络的生存期。（对） 4、美国军方最先开始无线传感器网络技术的研究。（对） 三、选择题
1、最先开始无线传感器网络技术的研究的国家是（B） A中国B美国C日本D韩国 2、无线传感器网络的特点包括（C） （1）可快速部署 （2）可自组织 （3）隐蔽性强和高容错性 （4）成本高，代价大 A （1）（2）（4） B （2）（3）（4） C （1）（2）（3） D（1）（3）（4） 3、将“信息社会技术”作为优先发展领域之一。其中多处涉及对WSN 的研究，启动了EYES 等研究计划的组织是（D） A日本总务省 B韩国信息通信部 C美国国防部 D欧盟 4、与无线传感器网络的兴起无关的技术是（A） A虚拟运营技术 B无线通信 C片上系统（SOC） D低功耗嵌入式技术
无线传感器网络技术试题
1. 传感器网络的三个基本要素：传感器、感知对象、用户(观察者) 2. 传感器网络的基本功能：协作式的感知、数据采集、数据处理、发布感知信息 3. 无线传感器节点的基本功能：采集数据、数据处理、控制、通信 4. 传感节点中处理部件用于协调节点各个部分的工作的部件。 5. 基站节点不属于传感器节点的组成部分 6. 定向扩散路由机制可以分为三个阶段：兴趣扩展阶段、梯度建立阶段、路径加强阶段 7. 无线传感器网络特点：大规模网络、自组织网络、可靠的网络、以数据为中心的网络、应用相关的网络 8. NTP时间同步协议不是传感器网络的的时间同步机制。 9. IEEE 802.15.4标准主要包括：物理层。介质访问控制层 10. 从用户的角度看，汇聚节点被称为网关节点。 11. 数据融合的内容主要包括：多传感器的目标探测、数据关联、跟踪与识别、情况评估和预测 13. 传感器网络的电源节能方法：_休眠（技术）机制、__数据融合 14. 分布式系统协同工作的基础是时间同步机制 15. 无线网络可以被分为有基础设施的网络与没有基础设施的网络，在无线传感器网络，Internet 网络，WLan 网络，拨号网络中，无线传感器网络属于没有基础设施的网络。 16. 传感器网络中，MAC层与物理层采用的是IEEE制定的IEEE 802.15协议 17. 分级结构的传感器网络可以解决平面结构的拥塞问题 18. 以数据为中心特点是传感器网络的组网特点，但不是Ad-Hoc的组网特点 19. 为了确保目标节点在发送ACK过程中不与其它节点发生冲突，目标节点使用了SIFS帧间间隔 20. 典型的基于竞争的MAC协议为CSMA
弱电安防监控系统方案
目录 1.系统概述...................................................................................................................... - 0 - 2.系统需求分析.............................................................................................................. - 0 - 3.编制依据...................................................................................................................... - 1 - 4.方案设计...................................................................................................................... - 1 - 本系统在楼内的主要出入口、地下车库、收费处、电梯厅、电梯轿厢等处设有监控点共计291处。其中首层大厅安装的是高速快球摄像机，地下车库安装有4台枪机，电梯内安装的是电梯专用摄像机，其余地方都为彩色固定半球摄像机。本系统采用模拟+数字的视频监控方式，在弱电井设置网络视频服务器、交换机，通过前端模拟摄像机采集信号，经视频服务器转换为数字信号后通过交换机传输至一层安防控制中心。存储系统由3台服务器，3套磁盘阵列设备组成。................................................................................................... - 1 -本套系统有以下特点：....................................................................................................... - 1 - 4.1系统架构...................................................................................................................... - 3 - 4.2产品性能介绍.............................................................................................................. - 5 - 4.2.1摄像机.......................................................................................................... - 5 - 4.2.2视频传输...................................................................................................... - 5 - 4.2.3视频存储...................................................................................................... - 6 - 4.2.4视频切换，管理与控制.............................................................................. - 7 - 4.2.5显示.............................................................................................................. - 8 - 4.3系统设备主要性能指标.............................................................................................. - 8 -
无线传感器网络覆盖技术
无线传感器网络覆盖技术 谭慧婷15040024 1.覆盖技术理论基础 覆盖问题是无线传感器网络配置首先要面对的基本问题，它反映了一个无线传感器网络某区域被检测和跟踪的状况。现有的研究结果，很多都是致力于解决传感器网络的部署和检测以及覆盖与连接的关系等方面的问题。 覆盖问题可以表述成不同的理论模型，甚至在平面几何里就能找到相应的解决方案。即使简单地只从数学上来考虑，在部署传感器节点的时候，我们必须知道怎样用相同的节点数覆盖尽可能大的区域。 为了对网络的覆盖问题先有一个初步的认识，这里我们提出一个几何问题-艺术馆问题来理解。 假设艺术馆的主人想在场馆内放置监视器来防止盗窃。假定相机可以有360度的视角而且可以极大速度旋转，相机可以监视任何位置，视线不受影响。 关于实现这个想法存在两个问题需要回答：首先就是到底需要多少台相机；其次，这些相机应当放置在哪些地方才能保证馆内每个点至少被一台相机监视到。
一个简单的办法就是将多边形分成不重叠的三角形，每个三角形里面放置一个相机。通过这个方法，我们可以得到最佳分布应该如下图，放置两个相机相机足以覆盖整个艺术馆。 相机1 我们可以知道无线传感器网络的覆盖问题在本职上和上面的几何问题是一致的：需要知道是否某个区域被充分覆盖以及完全处于监视之下。 但我们也必须认识到，几何研究的结果为理解传感器覆盖问题提供了一个理论背景，但这样的求解办法是无法直接应用到无线传感器网络。 因为： 1. 监视器可以看到无穷远的地方只要没有障碍物阻挡，但是 传感器节点存在最大感应范围； 2. 无线传感器网路没有类似监视器之间固定的基础设施，其 拓扑结构可能随时变化。 2.覆盖的感知模型 在讨论节点如何布置之前，需要先知道传感器节点的感知模型。目前主要是两种。
方案-XX安防系统建设方案
XXXX安防系统建设方案 一、任务来源 XX创办于XX年，校园占地面积XX万平方米，建筑面积XX万平方米，固定资产XX亿元，其中教学仪器设备近XX万元。然而校园一直没有建设覆盖全校的XX系统，无法给全校师生提供全方位安全保障。 根据教育部建设“平安校园”的要求，必须建设具有高技术水平的、重点覆盖全面控制的、满足学校未来一段时间发展需要的安防系统。根据学校会议决定，立即建设XXXX安防综合管理系统。 二、设计依据 1、GB50348-2004《安全防范工程技术规范》 2、GB/T50314-2000《智能建筑设计标准》 3、GB50198-94 4、GBJ115-87 5、GA/T367-2001 6、GA/T75-94 7、GBJ42-81 8、GA/308-2001 9、GA/T70-2004 10、GB/T74-2000 11、JGJ/T16-92 12、GYJ253-88《民用闭路监控电视系统工程技术规范》《工业电视监控系统工程设计规范》《视频安防监控系统技术要求》 《安全防范工程程序与要求》 《工业企业通迅设计规范》 《安全防范系统验收规则》 《安全防范工程费用预算编制办法》《安全防范系统通用图形符号》 《民用建筑电气设计规范》 《建筑电气安装工程质量检验评定标准》 13、GBJ232-90，92《电气装置安装工程施工及验收规范》 14、GA/T368-2001《入侵报警系统技术要求》 15、GA/T6692006《城市监控报警联网系统通用技术要求》 16、GB/T28181《安全防范视频监控联网系统信息传输、交换、控制技术要求》 17、XXXX提出的需求
三、指导思想 以科学发展观为指导，按照建设现代安全防控体系的总体要求，将XX建设作为校园安防管理创新、平安高校建设的重要内容。以公共场所和重点部位视频监控、安全管理信息化、出入口人车管理系统建设为重点，广泛动员学校各方面力量，充分发挥各部门职能作用，全力打造全方位、全天候、立体化的科技防范网络体系，进一步提升校园社会治安防控水平，为保障和促进学校又好又快发展创造稳定的治安环境。 四、系统总体要求 一方面，系统必须更符合XXXX大学信息化建设的要求，并成为未来校园信息化平台的一部分。大学校园综合信息平台是以网络为基础，利用先进的信息化手段和工具，实现从硬件环境、教学资源、到教学活动、最后到管理的全部数字化，在传统校园的基础上，构建一个数字空间以拓展现实校园的时间和空间维度，从而提升了传统校园的效率，扩展了传统校园的功能，最终实现教育过程的全面信息化。作为管理层面来讲包括党务和校务、总务、教务三大块。安全管理平台是学校党务和校务的重要性组成部分，是师生获得安全保障、安全服务、安全救助的重要途径。 另一方面，校园综合信息平台建设是分阶段、分层次的，它经历的是由硬到软、由下而上、螺旋上升的建设过程。安全保障作为一所大学基本的办学保障，是一所学校办学必须的条件之一，因此安全管理平台建设已经迫在眉睫，必须先行启动。XXXX大学作为一所高校，对安防系统防护等级要求较高完整的安防系统包括动态监控系统、安全管理系统、门车管理系统等三大部分组成。安防信息化建设作为全校信息化建设的子系统，建成后将为完善高校信息化做出积极贡献。其中，视频监控系统作为整个安防系统的核心，肩负着整个校园安全防范和管理工作。 1.1集成管理方面的需求 在系统管理上，安防各子系统相对独立运行，但集成在一个安防综合管理平台上。
无线传感器网络与RFID技术复习题
无线传感器网络与RFID技术复习题 一、填空题 1、传感器网络的三个基本要素：传感器、感知对象、观察者（用户）。 2、无线通信物理层的主要技术包括：介质的选择、频段的选择、调制技术和扩频技术。 3、无线传感器网络特点：大规模网络、自组织网络、可靠的网络、以数据为中心的网络、应用相关的网络。 4、无线传感器网络的关键技术主要包括：网络拓扑控制、网络协议、时间同步、定位技术、数据融合及管理、网络安全、应用层技术等。 5、传感器节点由传感器模块、处理器模块、无线通信模块和能量供应模块四部分组成。 6、无线传感器网络的组成模块分为：通信模块、传感模块、计算模块、存储模块和电源模块。 7、传感器网络的支撑技术包括：时间同步、定位技术、数据融合、能量管理、安全机制。 8、传感器节点通信模块的工作模式有发送、接收和空闲。 9、传感器节点的能耗主要集中在通信模块。 10、当前传感器网络应用最广的两种通信协议是：zigbee、IEEE802.15.4。 11、ZigBee主要界定了网络、安全和应用框架层，通常它的网络层支持三种拓扑结构：星型(Star)结构、网状（Mesh）结构、簇树型（Cluster Tree）结构。 12、根据对传感器数据的操作级别，可将数据融合技术分为以下三类：特征级融合、数据级融合、决策级融合。 13、信道可以从侠义和广义两方面理解，侠义的信道（信号输出的媒质），分为（有线信道和无线信道）；广义信道（包括除除传输媒质还包括有关的转换器）广义信道按照功能可以分为（模拟信道）和（数字信道）。 14、无线传感器网络可以选择的频段有：868MHZ、915MHZ、2.4GHZ、5.8GHZ。 15、无线通信物理层的主要技术包括：介质的选择、频段的选择、调制技术和扩频技术。 16、IEEE 802.15.4标准主要包括：物理层和MAC层的标准。 17、传感器网络中常用的测距方法有：到达时间/到达时间差(ToA/TDoA)、接收信号强度指示(RSSI)、到达角(AoA)。
无线传感网络技术与发展趋势的分析
无线传感网络技术与发展趋势的分析 引言 无线网络传感技术给人们的生活创造了很多的乐趣，也为信息的有效、及时的传递起到一定的促进作用，人们越来越依赖无线传感网络技术为其生活带来的舒适和方便，无线网络传感技术越来越受到社会各界的广泛关注，下文主要讲述了无线传感网络技术的概念、无线传感网络技术的发展现状以及无线传感网络技术的应用和发展。 1无线传感网络技术的概念 1.1无线传感网络技术是最近一种新型的网络技术，而且它一出现，就受到了世界各个国家的广泛关注和赞誉，无线传感网络技术是集多项科学技术于一身，多种高难度的知识相互交叉产生的具有高科技的、比较热门的、前沿的技术。 1.2无线传感网络技术集中了嵌入式计算、无线通信技术、传感器、现代网络和分散式的信息处理等高科技，实现了人们无论在何时何地都能够接收到来自网络的比较真实可靠的大量的信息的愿望，无线传感网络技术真正体现了信息无处不在的理念。 1.3无线传感网络在产生之初就以一种势不可挡的气势横扫世界的各个领域，无线传感网络的发展前景备受世人的关注，其应用和发展必定给人们的工作和生活带来极大的影响，它的辉煌应用成就了它的无双的地位，无线传感网络技术应用于军事领域，成为军事领域比较关键的高科技技术，但是无线网络不仅应用在军事领域，它对世界各
个领域的影响也是不可小觑的。 2无线传感网络技术的发展现状 2.1无线传感网络技术很受大众的喜欢与它的高科技的发展是分不开的，而且许多国家也很重视它的发展，世界各国的工业界、高科技界和学术界对无线传感网络的发展展开了猛烈的攻势，希望可以通过靠科技技术的结合实现无线传感网络技术的进步，许多国家还将无线传感网络技术列入国家的重点研究技术，而且一些周刊和杂志对无线网络的评价也很高，认为无线传感网络技术是未来引领世界计算机进步的主要技术。 2.2无线传感网络技术在我国的发展还很缓慢，这主要是由于无线传感网络技术在我国出现的时间比较晚，无线传感网络技术在我国的研究方案中还处在初级阶段，与西方一些发达国家相比，存在严重的滞后性，我国在无线传感网络技术上的研究主要局限在仿真计算和网络协议等，在人们的生活和军事中的应用还很少，而且无线网络现在已经可以用来作环境监测，我国却没有将无线传感网络技术应用到实处。 2.3目前，中国的未来技术研究方向中有几项是专门针对无线传感网络技术进行直接论述的，而且在一些重大会议的决策里而，也将无线传感网络技术列为三大前沿信息技术，无线传感网络技术中的自发组织网络技术和智能感知技术都成为中国重点信息技术研究，无线传感网络技术在我国如此重视的情况下一定会有所成就，无线传感网络技术也成为社会信息技术发展的必然，在我国，信息技术领域广泛地
矿用无线通信系统使用说明书
矿用无线通信系统使用说明书
1、概述： 1.1 用途 KT201矿用无线通信系统做为新一代的矿井无线传输系统，采用WIFI与TCP/IP技术相结合，在煤矿井下实现了无线数据的高速传输，为煤矿提供了一个宽带无线传输平台。该系统根据长春东煤机电研究所企业标准《Q/DMJD 30-2011 KT201矿用无线通信系统》研制、生产、配套和使用，以光纤网络为骨干(接入现有工业环网或独立组网)，以无线网络延伸，在煤矿井下设立若干基站，通过无线通信手段，为实现人员的语音通信、人员管理、数字化视频监控及环境监测等提供了一个共用的平台；也为实现生产调度、应急救援与安全监控与督察提供了良好的应用基础。系统可根据用户的实际需要灵活配置，它的推广应用将使煤矿通信走上新的台阶。 KT201矿用无线通信系统可根据煤矿企业的不同需求，配备不同的功能模块从而实现不同的功能。通过无线通信系统，可以实现煤矿企业的通信一体化、管理一体化，数据交换的一体化、数据存储与使用的一体化。避免了采用多个单独系统所带来的数据格式不一、交换效率低下、安全性差等诸多问题。 KT201矿用无线通信系统分地面和井下两部分。地面部分由无线控制主机、语音服务器、KJJ127矿用隔爆兼本安型环网交换机以及专用监控软件组成，可配中英文打印机、远程终端、大屏幕投影仪等设备构成功能强大的信息处理中心。井下部分主要由KJJ127矿用隔爆兼本安型环网交换机、KT201-F矿用隔爆兼本安型无线基站、DXB18矿用隔爆型电池箱、佩带在作业人员身上的KT201-S矿用本安型手机以及矿用通信光缆等构成通信网络。 1.2 系统型号含义如下图1所示： 1.3使用环境条件
无线传感器网络练习题(1)
一、填空 1.无线传感器网络系统通常包含汇聚节点、传感器节点、管理节点。 2.传感器节点一般由通信模块、传感器模块、存储模块和电源模块 组成。 3.无线传感器节点的基本功能是：采集数据、数据处理、控制和通 信。 4.传感器节点通信模块的工作模式有发送、接收和空闲。 5.无线通信物理层的主要技术包括介质的选择、频段的选择、调制 技术和扩频技术。 6.扩频技术按照工作方式的不同，可以分为四种：直接序列扩频、 跳频、跳时和宽带线性调频扩频。 7.目前无线传感器网络采用的主要传输介质包括无线电波、光纤、 红外线等。 8.无线传感器网络可以选择的频段有：868MHz、915MHz、和5GHz。 9.传感器网络的电源节能方法：休眠机制、数据融合。 10.根据对传感器数据的操作级别，可将数据融合技术分为一下三类： 决策级融合、特征级融合、数据级融合。 11.根据融合前后数据的信息含量分类（无损失融合和有损失融合） 12.根据数据融合与应用层数据语义的关系分类（依赖于应用的数据 融合、独立于应用的数据融合、结合以上两种技术的数据融合）13.定向扩散路由机制可以分为三个阶段：兴趣扩散、梯度建立、路 径加强。
14.无线传感器网络的关键技术主要包括：时间同步机制、数据融合、 路由选择、定位技术、安全机制等。 15.无线传感器网络通信安全需求主要包括结点的安全保证、被动抵 御的入侵能力、主动反击入侵的能力。 16.标准用于无线局域网，标准用于低速无线个域网。 17.规定三种帧间间隔：SIFS、PIFS、DIFS。 18.标准为低速个域网制定了物理层和MAC子层协议。 19.ZigBee主要界定了网络、安全和应用框架层，通常它的网络层支 持三种拓扑结构：网状网络、树形网络、星型网络。 20.传感器网络中常用的测距方法有：接收信号强度指示、到达时间 差、到达角。 21.ZigBee网络分4层分别为：物理层、网络层、应用层、数据链路 层。 22.与传统网络的路由协议相比，无线传感器网络的路由协议具有以 下特点：能量优先、基于局部拓扑、以数据为中心、应用相关。 23.数据融合的内容主要包括：目标探测、数据关联、跟踪与识别、 情况评估与预测。 24.无线传感器网络信息安全需求主要包括数据的机密性、数据鉴别、 数据的完整性、数据的实效性。 25.传感器结点的限制条件是电源能量有限、通信能力有限、计算和 存储能力有限。
安防监控系统施工方案
安防监控系统施工方案 对于闭路电视监控系统来说，施工的难点主要在于设备安装定位的问题。 一般说来新建建筑物都具高装饰性特点，为保证系统前端摄像机等设备、特别是支架的安装工艺不能破坏整体建筑物装饰效果，故在系统前端设备安装方面，应考虑某些场所装饰性极强的特点，及时根据现场环境调整摄像机支架安装高度和安装方式。例如：吸顶安装方式、墙装安装方式等。 同时在对定焦摄像机安装时还应充分考虑：安装高度对角度的影响，所以应根据视场监视的角度进行摄像机安装定位。 摄像机的安装须考虑与环境光线的关系，勘测摄像机的安装位置，记录一天的光照度变化和夜间能提供的光照度情况，观察视场范围和图像质量，并在平面图上标记出摄像机及出线口的位置。大楼内的光照度基本稳定，对摄像机要求不高，对于大堂内的摄像机，由于其受外界阳光的影响较大，安装时主要考虑逆光问题，在位置选择上，不可正对大门，一般以45O角为宜，必要时应进行现场模拟实验，具体位置须带上摄像机及显示器现场测定。 摄像机安装时须考虑与其他安保子系统探测器的联动关系，这些探测器包括：微波红外探测器（吸顶式、挂墙式）、紧急按钮等设备的安装位置，以提高摄像机的使用效率，特别是球型摄像机的效率。 1.1 系统设备安装前的检查 1)安装环境的检查 1.监控室设备的安装要求土建及装修完毕； 2.监控室的温湿度、光照度、通风等条件要满足设备安装要求； 3.摄像机的安装要求周边无干扰源、震动等。 2)设备的检查 4.备外形完整，内外表面漆层完好； 5.设备单个通电检查，无异常情况； 6.小范围内控制系统通电联合检查，各个设备无异常情况。 3)线缆的检查 7.线缆的布放是否符合设计要求； 8.线缆的通断检查； 9.线缆的短路检查；
安防系统方案
安防系统方案 学校历来是安全防范的重点单位，随着社会治安形势的不断变化，一些令人震惊的恶性事件唤醒了社会的关注，因为学生安全关系千家万户，关系整个社会的和谐稳定。视频监控系统作为校园科技防范的核心，将实现全覆盖、与公安系统联动。 校园监控系统与其它行业相比，具有明显的特点，主要表现在： 1）学校作为特殊公共场所，场地分散、面积大、管理人员少、学生众多，因此要求监控设施的安装及维护方便，系统支持多种网络传输模式。 2）要求能远程报警，一旦发生人员入侵、暴力事件发生时，可通过网络将警情上传到网络监控中心，并将图像自动切换到现场，自动录像，便于及时采取措施。 3）系统设备型号众多，跨越时间较长。各学校已建成的监控系统包含了众多品牌、型号的各类产品，而这些产品没有统一的规范和协议，无法做到互联互通。 设计目标 1) 建立一套全IP构架模式的安防平台，能充分满足中国药科大学平安校园建设的需要，全IP视频监控系统是实现高性价比的高清视频监控系统的基石； 2) 建立一套统一的以视频为主的安防管理平台，实现门禁、巡更、报警及其它子系统的集成。依托视频监控专网作传输通道，在监控终端上浏览各前端视频信号，通过统一的界面控制所有的IP摄像机、硬盘录像机、视频服务器等设备，实现本需求中的所有系统功能； 3) 对前端图像设备应具备兼容性，包括对硬盘录像机、视频服务器、网络摄像机等数字图像设备的兼容；能够实现多种模式的图像采集、压缩、显示、报警联动、控制、远程存储回放、远程管理等；能够兼容的数字图像设备应包括国内主流品牌的数字图像设备，在前端设备兼容方面应实现安全开放式的兼容； 4) 建立一套智能化管理平台，依靠视频监控系统、智能分析、报警系统等子系统及其之间的系统联动，为用户及时提供异常事件的监控信息，将被动监控化为主动，做到防患于未然；
《无线传感器网络》试题.
《无线传感器网络》试题 一、填空题（每题4分，共计60分） 1、传感器网络的三个基本要素：传感器，感知对象，观察者 2、传感器网络的基本功能：协作地感知、采集、处理和发布感知信息 3、无线传感器节点的基本功能：采集、处理、控制和通信等 4、传感器网络常见的时间同步机制有： 5、无线通信物理层的主要技术包括：介质的选择、频段的选择、调制技术和扩频技术 6扩频技术按照工作方式的不同，可以分为以下四种： ：直接序列扩频、跳频、跳时、宽带线性调频扩频 7、定向扩散路由机制可以分为三个阶段：周期性的兴趣扩散、梯度建立和路径加强 8、无线传感器网络特点：大规模网络、自组织网络、可靠的网络、以数据为中心的网络、应用相关的网络 9、无线传感器网络的关键技术主要包括：网络拓扑控制、网络协议、时间同步、定位技术、数据融合及管理、网络安全、应用层技术等 10、IEEE 802.15.4标准主要包括：物理层和MAC层的标准 11、简述无线传感器网络后台管理软件结构与组成：后台管理软件通常由数据库、数据处理引擎、图形用户界面和后台组件四个部分组成。 12、数据融合的内容主要包括：多传感器的目标探测、数据关联、跟踪与识别、情况评估和预测 13、无线传感器网络可以选择的频段有：868MHZ、915MHZ、2.4GHZ 5GHZ
14、传感器网络的电源节能方法：休眠机制、数据融合等， 15、传感器网络的安全问题：(1) 机密性问题。(2) 点到点的消息认证问题。(3) 完整性鉴别问题。 16、802.11规定三种帧间间隔：短帧间间隔SIFS，长度为28 s 、点协调功能帧间间隔PIFS长度是SIFS 加一个时隙(slot)长度，即78 s 分布协调功能帧间间隔DIFS ，DIFS长度=PIFS +1个时隙长度，DIFS 的长度为128 s 17、任意相邻区域使用无频率交叉的频道是，如：1、6、11频道。 18、802.11网络的基本元素SSID标示了一个无线服务，这个服务的内容包括了：接入速率、工作信道、认证加密方法、网络访问权限等 19、传感器是将外界信号转换为电信号的装置，传感器一般由敏感元件、转换元件、转换电路三部分组成 20、传感器节点由传感器模块、处理器模块、无线通信模块和能量供应模块四部分组成 二、基本概念解释（每题5分，共40分） 1.简述无线网络介质访问控制方法CSMA/CA的工作原理 CSMA/CA机制: 当某个站点（源站点）有数据帧要发送时，检测信道。若信道空闲，且在DIFS时间内一直空闲，则发送这个数据帧。发送结束后，源站点等待接收ACK确认帧。如果目的站点接收到正确的数据帧，还需要等待SIFS时间，然后向源站点发送ACK确认帧。若源站点在规定的时间内接收到ACK确认帧，则说明没有发生冲突，这一帧发送成功。
安防监控系统技术方案
****** 项目*******安防监控系统实施方案 人：日期：编制 审核日期：人： 批日期：准：
2 / 21 目录 1. 总则 ....................................... 错误！未指定书签。 2．系统建设概述 ............................... 错误！未指定书签。 3. 执行标准 ................................... 错误！未指定书签。................................... 4. 现场环境错误！未指定书签。................................... ．供货范围 5错误！未指定书签。................................... ．交付时间 6错误！未指定书签。................................... 技术要求 7. 错误！未指定书签。............................. 8. 检验方法和要求错误！未指定书签。............................... 9. 性能保证条款错误！未指定书签。 ........................ 技术资料及交付进度10. 错误！未指定书签。................................ 11. 包装及交货错误！未指定书签。 ................ 12. 售后服务要求及服务内容条款错误！未指定书签。 总则 1.
根据**********公司********项目***************，对厂区的 事态、人流等状况进行宏观监视，以便于随时掌握各种活动情况。在特殊情况下，可以对入侵、防盗所发现的异常情况进行监视取证。在人们无法直接观察的场合实时、形象、真实地反映被监视控制对象的画面，通过本安防监控系统方案，安装监控有效地威慑和预防事件的发生，提高技防装备水平与管理档次，以及对系统设备的功能设计、结构、性能、安装和试验等方面的进行相关技术要求。 1.1 本方案规定了监控系统的最低限度的技术要求，并未规定 所有的技术要求和适用特性，卖方根据本方案所列基本要求和有关标准规范提供高质量产品及相关服务，且必须满足国内有关安全、环保等强制性标准。卖方提供的产品必须是全新制造的产品，并且是当前国际技术和工艺最先进的产品。 1.2 遵循本方案的要求并不能解除任何卖方的责任、保证和合 同等规定的其它义务。 1.3 本方案所使用的标准如遇与卖方所执行的标准发生矛盾时，按较高标准执行。 1.4 在合同签订后，我方有权提出因标准、规程和规范发生变 化而产生的修订要求，具体事宜由双方协商确定。 1.5 卖方入厂施工前比须经过我方安全教育等相关部门审批。 施工现场比须服从我方的相关管理规定。由卖方自身造成的一切人员伤害等不安全事故，由卖方全权负责，并在第一时间通报我