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33-500: Many radiolocation systems use TOA measurements to perform geopositioning via true-range multilateration . The true range or distance can be directly calculated from the TOA as signals travel with a known velocity . TOA from two base stations will narrow a position to a position circle ; data from a third base station is required to resolve the precise position to a single point. TDOA techniques such as pseudorange multilateration use

66-408: A number of impairments can occur: absorption, refraction, shadowing, and reflection. Absorption is negligible for radio propagation in air at frequencies less than about 10 GHz, but becomes important at multi-GHz frequencies where rotational molecular states can be excited. Refraction is important at long ranges (tens to hundreds of kilometers) due to gradients in moisture content and temperature in

99-427: A short time scale, a signal must use a broad bandwidth. For example, to create a pulse of about 1 ns duration, roughly sufficient to identify location to within 0.3 m (1 foot), a bandwidth of roughly 1 GHz is required. In many regions of the radio spectrum, emission over such a broad bandwidth is not allowed by the relevant regulatory authorities, in order to avoid interference with other narrowband users of

132-418: A surveillance system calculates the time differences ( τ i {\displaystyle \tau _{i}} for i = 1 , 2 , . . . , m − 1 {\displaystyle i=1,2,...,m-1} ) of wavefronts touching each receiver. The TDOA equation for receivers i {\displaystyle i} and 0 {\displaystyle 0}

165-415: A transmitter from a single receiver requires that both the transmitted (or backscattered) power from the object to be located are known, and that the propagation characteristics of the intervening region are known. In empty space, signal strength decreases as the inverse square of the distance for distances large compared to a wavelength and compared to the object to be located, but in most real environments,

198-715: Is (where the wave propagation speed is c {\displaystyle c} and the true vehicle-receiver ranges are R 0 {\displaystyle R_{0}} and R i {\displaystyle R_{i}} ) c τ i = c T i − c T 0 , c τ i = R i − R 0 . {\displaystyle {\begin{aligned}c\,\tau _{i}&=c\,T_{i}-c\,T_{0},\\c\,\tau _{i}&=R_{i}-R_{0}.\end{aligned}}} The quantity c T i {\displaystyle c\,T_{i}}

231-786: Is based on TOA of signals from satellites at known positions. Radiolocation is also used in cellular telephony via base stations . Most often, this is done through trilateration between radio towers . The location of the Caller or handset can be determined several ways: The first two depend on a line-of-sight , which can be difficult or impossible in mountainous terrain or around skyscrapers . Location signatures actually work better in these conditions however. TDMA and GSM networks such as Cingular and T-Mobile use TDOA. CDMA networks such as Verizon Wireless and Sprint PCS tend to use handset-based radiolocation technologies, which are technically more similar to radionavigation. GPS

264-548: Is employed in a wide variety of industrial and military activities. Radar systems often use a combination of TOA and AOA to determine a backscattering object's position using a single receiver. In Doppler radar , the Doppler shift is also taken into account, determining velocity rather than location (though it helps determine future location). Real Time Location Systems RTLS using calibrated RTLS, and TDOA, are commercially available. The widely used Global Positioning System ( GPS )

297-526: Is often combined with calibration measurements ("fingerprinting") to improve accuracy. TOA and AOA measurements are also subject to multipath errors, particularly when the direct path from the transmitter to receiver is blocked by an obstacle. Time of arrival measurements are also most accurate when the signal has distinct time-dependent features on the scale of interest—for example, when it is composed of short pulses of known duration—but Fourier transform theory shows that in order to change amplitude or phase on

330-691: Is often termed a pseudo-range. It differs from the true range between the vehicle and station i {\displaystyle i} by an offset, or bias, which is the same for every signal. Differencing two pseudo-ranges yields the difference of the same two true-ranges. Figure 4a (first two plots) show a simulation of a pulse waveform recorded by receivers P 0 {\displaystyle P_{0}} and P 1 {\displaystyle P_{1}} . The spacing between E {\displaystyle E} , P 1 {\displaystyle P_{1}} and P 0 {\displaystyle P_{0}}

363-512: Is one of those technologies. Composite solutions, needing both the handset and the network include: Initially, the purpose of any of these in mobile phones is so that the public safety answering point (PSAP) which answers calls to an emergency telephone number can know where the caller is and exactly where to send emergency services . This ability is known within the NANP ( North America ) as wireless enhanced 911 . Mobile phone users may have

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396-706: Is such that the pulse takes 5 time units longer to reach P 1 {\displaystyle P_{1}} than P 0 {\displaystyle P_{0}} . The units of time in Figure ;4 are arbitrary. The following table gives approximate time scale units for recording different types of waves: The red curve in Figure 4a (third plot) is the cross-correlation function ( P 1 ⋆ P 0 ) {\displaystyle (P_{1}\star P_{0})} . The cross-correlation function slides one curve in time across

429-488: Is the process of finding the location of something through the use of radio waves . It generally refers to passive, particularly radar —as well as detecting buried cables, water mains , and other public utilities . It is similar to radionavigation in which one actively seeks its own position; both are types of radiodetermination . Radiolocation is also used in real-time locating systems (RTLS) for tracking valuable assets. An object can be located by measuring

462-409: Is the same as the Figure 4a example. Again, the peak in the cross-correlation occurs at τ 1 = 5 {\displaystyle \tau _{1}=5} . Figure 4c is an example of a continuous, narrow-band waveform from the emitter. The cross-correlation function shows an important factor when choosing the receiver geometry. There is a peak at time = 5 plus every increment of

495-536: Is – according to Article 1.49 of the International Telecommunication Union's (ITU) Radio Regulations (RR) – defined as «A radiodetermination-satellite service used for the purpose of radiolocation. This (radiocommunication) service may also include the feeder links necessary for its operation .» The radiolocation-satellite service distinguishes basically For example military radar sensors in earth satellites operate in

528-638: The radiocommunication service in which it operates permanently or temporarily. In accordance with ITU Radio Regulations (article 1) this type of radio station might be classified as follows: Radiodetermination station (article 1.86) of the radiodetermination service (article 1.40 ) Radiolocation mobile station is – according to article 1.89 of the International Telecommunication Union's (ITU) ITU Radio Regulations (RR) – defined as "A radio station in radiolocation service intended to be used while in motion or during halts at unspecified points." Each radiolocation station shall be classified by

561-421: The oscillators of the involved transmitters is not viable, hence the clocks differ, then applying the measurement as a two ways travel to the receiver and mirrored back to the transmitter compensates for some of the phase differences between the oscillators involved. This concept is applied with the real-time locating system (RTLS) concept as defined in the international standard ISO/IEC FCD 24730-5. Assume

594-489: The radiolocation-satellite service n this service. The allocation of radio frequencies is provided according to Article 5 of the ITU Radio Regulations (edition 2012). In order to improve harmonisation in spectrum utilisation, the majority of service-allocations stipulated in this document were incorporated in national Tables of Frequency Allocations and Utilisations which is within the responsibility of

627-546: The time of arrival (TOA), when the time of transmission and speed of propagation are known. Combining TOA data from several receivers at different known locations (time difference of arrival, TDOA) can provide an estimate of position even in the absence of knowledge of the time of transmission. The angle of arrival (AOA) at a receiving station can be determined by the use of a directional antenna, or by differential time of arrival at an array of antennas with known location. AOA information may be combined with distance estimates from

660-411: The appropriate national administration. The allocation might be primary, secondary, exclusive, and shared. A radiolocation land station is – according to article 1.90 of the International Telecommunication Union's (ITU) ITU Radio Regulations (RR) – defined as "a radio station in radiolocation service not intended to be used while in motion." Each radiolocation station shall be classified by

693-638: The atmosphere. In urban, mountainous, or indoor environments, obstruction by intervening obstacles and reflection from nearby surfaces are very common, and contribute to multipath distortion: that is, reflected and delayed replicates of the transmitted signal are combined at the receiver. Signals from different paths can add constructively or destructively: such variations in amplitude are known as fading . The dependence of signal strength on position of transmitter and receiver becomes complex and often non-monotonic, making single-receiver estimates of position inaccurate and unreliable. Multilateration using many receivers

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726-413: The calculated location. If the phase noise is large enough, the phase detector can become unstable. Navigation systems employ similar, but slightly more complex, methods than surveillance systems to obtain delay differences. The major change is DTOA navigation systems cross-correlate each received signal with a stored replica of the transmitted signal (rather than another received signal). The result yields

759-449: The characteristics of received radio waves. The radio waves may be transmitted by the object to be located, or they may be backscattered waves (as in radar or passive RFID ). A stud finder uses radiolocation when it uses radio waves rather than ultrasound . One technique measures a distance by using the difference in the power of the received signal strength (RSSI) as compared to the originating signal strength. Another technique uses

792-402: The final step, subtracting the results of one cross-correlation from another, is not performed. Thus, the result is m {\displaystyle m} received signal time delays plus the user clock's bias ( T i {\displaystyle T_{i}} in equation  3 ). Radiolocation Radiolocation , also known as radiolocating or radiopositioning ,

825-438: The measured time difference between TOAs. The concept may be applied as well with IEEE 802.15.4a CSS as with IEEE 802.15.4aUWB modulation. As with TDOA, synchronization of the network base station with the locating reference stations is important. This synchronization can be done in different ways: Two-way ranging is a cooperative method for determining the range between two radio transceiver units. When synchronisation of

858-453: The number of cycles that pass by as the emitter moves. This only works for continuous, narrow-band waveforms because of the relation between phase θ {\displaystyle \theta } , frequency f {\displaystyle f} and time T {\displaystyle T} : The phase detector will see variations in frequency as measured phase noise , which will be an uncertainty that propagates into

891-476: The option to permit the location information gathered to be sent to other phone numbers or data networks, so that it can help people who are simply lost or want other location-based services . By default, this selection is usually turned off, to protect privacy . Radiolocation service (short: RLS ) is – according to Article 1.48 of the International Telecommunication Union's (ITU) Radio Regulations (RR) – defined as "A radiodetermination service for

924-417: The other and returns a peak value when the curve shapes match. The peak at time = 5 is a measure of the time shift between the recorded waveforms, which is also the τ {\displaystyle \tau } value needed for equation  3 . Figure 4b shows the same type of simulation for a wide-band waveform from the emitter. The time shift is 5 time units because the geometry and wave speed

957-413: The purpose of radiolocation", where radiolocation is defined as: "radiodetermination used for purposes other than those of radionavigation." This radiocommunication service is classified in accordance with ITU Radio Regulations (article 1) as follows: Radiodetermination service (article 1.40) The radiolocation service distinguishes basically Radiolocation-satellite service (short: RLSS )

990-422: The received signal time delay plus the user clock's bias (pseudo-range scaled by 1 / c {\displaystyle 1/c} ). Differencing the results of two such calculations yields the delay difference sought ( τ i {\displaystyle \tau _{i}} in equation  3 ). TOT navigation systems perform similar calculations as TDOA navigation systems. However,

1023-644: The spectrum. In the United States, unlicensed transmission is allowed in several bands, such as the 902-928 MHz and 2.4-2.483 GHz Industrial, Scientific, and Medical ISM bands , but high-power transmission cannot extend outside of these bands. However, several jurisdictions now allow ultrawideband transmission over GHz or multi-GHz bandwidths, with constraints on transmitted power to minimize interference with other spectrum users. UWB pulses can be very narrow in time, and often provide accurate estimates of TOA in urban or indoor environments. Radiolocation

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1056-582: The techniques previously described to establish the location of a transmitter or backscatterer. Alternatively, the AOA at two receiving stations of known location establishes the position of the transmitter. The use of multiple receivers to locate a transmitter is known as multilateration . Estimates are improved when the transmission characteristics of the medium is factored into the calculations. For RSSI this means electromagnetic permeability ; for TOA it may mean non-line-of-sight receptions. Use of RSSI to locate

1089-475: The waveform period. To get one solution for the measured time difference, the largest space between any two receivers must be closer than one wavelength of the emitter signal. Some systems, such as the LORAN C and Decca mentioned at earlier (recall the same math works for moving receiver and multiple known transmitters), use spacing larger than 1 wavelength and include equipment, such as a phase detector , to count

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