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45-477: RSSI is usually invisible to a user of a receiving device. However, because signal strength can vary greatly and affect functionality in wireless networking , IEEE 802.11 devices often make the measurement available to users. RSSI is often derived in the intermediate frequency (IF) stage before the IF amplifier. In zero-IF systems , it is derived in the baseband signal chain, before the baseband amplifier. RSSI output

90-547: A wireless access point (WAP) that also serves as a bridge to other networks such as a local area network or the Internet. Since wireless communication uses a more open medium for communication in comparison to wired LANs, the 802.11 designers also included encryption mechanisms: Wired Equivalent Privacy (WEP), no longer considered secure, Wi-Fi Protected Access (WPA, WPA2, WPA3), to secure wireless computer networks. Many access points will also offer Wi-Fi Protected Setup ,

135-425: A WDS must be configured to use the same radio channel and share WEP keys or WPA keys if they are used. They can be configured to different service set identifiers. WDS also requires that every base station be configured to forward to others in the system as mentioned above. There are two definitions for wireless LAN roaming: Time of arrival Time of arrival ( TOA or ToA ) is the absolute time instant when

180-586: A WDS over some other solutions is that it preserves the MAC addresses of client packets across links between access points. An access point can be either a main, relay, or remote base station. A main base station is typically connected to the wired Ethernet. A relay base station relays data between remote base stations, wireless clients or other relay stations to either a main or another relay base station. A remote base station accepts connections from wireless clients and passes them to relay or main stations. Because data

225-505: A group owner in the Wi-Fi Direct group. In one approach, the user sets up a P2P group owner manually. This method is also known as autonomous group owner ( autonomous GO ). In the second method, called negotiation-based group creation , two devices compete based on the group owner intent value. The device with higher intent value becomes a group owner and the second device becomes a client. Group owner intent value can depend on whether

270-719: A higher number of known nodes, as they rely on the Time of Arrival (TOA) and Angle of Arrival (AOA) of the signal for estimating the distance between the known nodes and the unknown node. However, the accuracy of these algorithms can be affected by environmental factors, such as signal interference, obstacles, and the density of nodes in the area. Factors like diffraction, reflection, scattering, and antenna type can significantly influence RSSI values. These variables need consideration for accurate indoor localization using RSSI. The RALE approach offers several advantages for indoor localization: Wireless LAN A wireless LAN ( WLAN )

315-406: A link for communication between wireless nodes. However, a power level metric like RCPI generally cannot comment on the quality of the link like other metrics such as travel time measurement ( time of arrival ). RSSI is commonly used in wireless communication protocols, such as Bluetooth and ZigBee , to estimate the distance between nodes. This estimation is essential for indoor localization and

360-553: A quick, but no longer considered secure, method of joining a new device to an encrypted network. Most Wi-Fi networks are deployed in infrastructure mode . In infrastructure mode, wireless clients, such as laptops and smartphones, connect to the WAP to join the network. The WAP usually has a wired network connection and may have permanent wireless connections to other WAPs. WAPs are usually fixed and provide service to their client nodes within range. Some networks will have multiple WAPs using

405-425: A radio signal emanating from a transmitter reaches a remote receiver. The time span elapsed since the time of transmission ( TOT or ToT ) is the time of flight (TOF or ToF). Time difference of arrival ( TDOA ) is the difference between TOAs. Many radiolocation systems use TOA measurements to perform geopositioning via true-range multilateration . The true range or distance can be directly calculated from

450-715: 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}}

495-431: Is a wireless computer network that links two or more devices using wireless communication to form a local area network (LAN) within a limited area such as a home, school, computer laboratory, campus, or office building. This gives users the ability to move around within the area and remain connected to the network. Through a gateway , a WLAN can also provide a connection to the wider Internet . Wireless LANs based on

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540-599: Is a set of all stations that can communicate with each other at PHY layer. Every BSS has an identification (ID) called the BSSID, which is the MAC address of the access point servicing the BSS. There are two types of BSS: Independent BSS (also referred to as IBSS), and infrastructure BSS. An independent BSS (IBSS) is an ad hoc network that contains no access points, which means they cannot connect to any other basic service set. In an IBSS

585-408: Is an 802.11 measure of the received radio frequency power in a selected channel over the preamble and the entire received frame , and has defined absolute levels of accuracy and resolution. RCPI is exclusively associated with 802.11 and as such has some accuracy and resolution enforced on it through IEEE 802.11k-2008 . Received signal power level assessment is a necessary step in establishing

630-439: Is forwarded wirelessly, consuming wireless bandwidth, throughput in this method is halved for wireless clients not connected to a main base station. Connections between base stations are done at layer-2 and do not involve or require layer-3 IP addresses. WDS capability may also be referred to as repeater mode because it appears to bridge and accept wireless clients at the same time (unlike traditional bridging). All base stations in

675-462: Is in contrast to Ethernet which uses carrier-sense multiple access with collision detection (CSMA/CD). The 802.11 specification includes provisions designed to minimize collisions because mobile units have to contend with the hidden node problem where two mobile units may both be in range of a common access point, but out of range of each other. A bridge can be used to connect networks, typically of different types. A wireless Ethernet bridge allows

720-513: Is nearly identical to the PHY of HiperLAN/2. In 2009, 802.11n was added to 802.11. It operates in both the 2.4 GHz and 5 GHz bands at a maximum data transfer rate of 600 Mbit/s. Most newer routers are dual-band and able to utilize both wireless bands. This allows data communications to avoid the crowded 2.4 GHz band , which is also shared with Bluetooth devices and microwave ovens . The 5 GHz band also has more channels than

765-405: Is often a DC analog level. It can also be sampled by an internal analog-to-digital converter (ADC) and the resulting values made available directly or via peripheral or internal processor bus. In an IEEE 802.11 system, RSSI is the relative received signal strength in a wireless environment, in arbitrary units. RSSI is an indication of the power level being received by the receiving radio after

810-403: Is often preferred due to its simplicity and the lack of need for synchronization or timestamping, as required in other methods like Time of Arrival (TOA). Various localization algorithms, such as anchor-based algorithms, employ RSSI. Anchor-based algorithms use nodes with known positions (anchors) to determine the location of an unknown node. The accuracy of these algorithms is enhanced by using

855-691: 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}}

900-706: 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

945-409: 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

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990-619: The IEEE 802.11 standards are the most widely used computer networks in the world. These are commonly called Wi-Fi , which is a trademark belonging to the Wi-Fi Alliance . They are used for home and small office networks that link together laptop computers , printers , smartphones , Web TVs and gaming devices with a wireless network router , which links them to the internet. Hotspots provided by routers at restaurants, coffee shops, hotels, libraries, and airports allow consumers to access

1035-525: The Independent Basic Service Set (IBSS). A Wi-Fi Direct network is a different type of wireless network where stations communicate peer-to-peer. In a peer-to-peer network wireless devices within range of each other can discover and communicate directly without involving central access points. In a Wi-Fi P2P group, the group owner operates as an access point and all other devices are clients. There are two main methods to establish

1080-599: The 2.4 GHz band, permitting a greater number of devices to share the space. Not all WLAN channels are available in all regions. A HomeRF group formed in 1997 to promote a technology aimed at residential use, but it disbanded in January 2003. All components that can connect into a wireless medium in a network are referred to as stations. All stations are equipped with wireless network interface controllers . Wireless stations fall into two categories: wireless access points (WAPs) and clients. WAPs are base stations for

1125-577: The RSSI value is 0 to 100. Another popular Wi-Fi chipset is made by Atheros . An Atheros-based card will return an RSSI value of 0 to 127 (0x7f) with 128 (0x80) indicating an invalid value. There is no standardized relationship of any particular physical parameter to the RSSI reading. The 802.11 standard does not define any relationship between RSSI value and power level in milliwatts or decibels referenced to one milliwatt (dBm) . Vendors and chipset makers provide their own accuracy, granularity, and range for

1170-893: The STAs are configured in ad hoc (peer-to-peer) mode. An extended service set (ESS) is a set of connected BSSs. Access points in an ESS are connected by a distribution system. Each ESS has an ID called the SSID which is a 32-byte (maximum) character string. A distribution system (DS) connects access points in an extended service set. The concept of a DS can be used to increase network coverage through roaming between cells. DS can be wired or wireless. Current wireless distribution systems are mostly based on WDS or Mesh protocols , though other systems are in use. The IEEE 802.11 has two basic modes of operation: infrastructure and ad hoc mode. In ad hoc mode, mobile units communicate directly peer-to-peer. In infrastructure mode, mobile units communicate through

1215-511: 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 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

1260-483: The actual power (measured as milliwatts, which can be expressed in terms of decibels relative to one milliwatt) and their range of RSSI values (from 0 to RSSI maximum, in arbitrary signal units "asu"). One subtlety of the 802.11 RSSI metric comes from how it is sampled—RSSI is acquired during only the preamble stage of receiving an 802.11 frame, not over the full frame. As early as 2000, researchers were able to use RSSI for coarse-grained location estimates. More recent work

1305-411: The antenna and possible cable loss. Therefore, the greater the RSSI value, the stronger the signal. Thus, when an RSSI value is represented in a negative form (e.g. −100), the closer the value is to 0, the stronger the received signal has been. RSSI can be used internally in a wireless networking card to determine when the amount of radio energy in the channel is below a certain threshold at which point

1350-413: 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

1395-439: The connection of devices on a wired Ethernet network to a wireless network. The bridge acts as the connection point to the wireless LAN. A wireless distribution system (WDS) enables the wireless interconnection of access points in an IEEE 802.11 network. It allows a wireless network to be expanded using multiple access points without the need for a wired backbone to link them, as is traditionally required. The notable advantage of

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1440-536: The internet with portable wireless devices. Norman Abramson , a professor at the University of Hawaii , developed the world's first wireless computer communication network, ALOHAnet . The system became operational in 1971 and included seven computers deployed over four islands to communicate with the central computer on the Oahu island without using phone lines. Wireless LAN hardware initially cost so much that it

1485-400: 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 the oscillators of the involved transmitters is not viable, hence the clocks differ, then applying the measurement as a two ways travel to

1530-437: The network card is clear to send (CTS). Once the card is clear to send, a packet of information can be sent. The end-user will likely observe an RSSI value when measuring the signal strength of a wireless network through the use of a wireless network monitoring tool like Wireshark , Kismet or Inssider . As an example, Cisco Systems cards have an RSSI maximum value of 100 and will report 101 different power levels, where

1575-453: 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

1620-417: 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

1665-422: 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,

1710-698: 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 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}

1755-417: The same SSID and security arrangement. In that case, connecting to any WAP on that network joins the client to the network, and the client software will try to choose the WAP that gives the best service, such as the WAP with the strongest signal. An ad hoc network is a network where stations communicate only peer-to-peer (P2P). There is no base and no one gives permission to talk. This is accomplished using

1800-475: 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

1845-428: The wireless device performs a cross-connection between an infrastructure WLAN service and a P2P group, available power in the wireless device, whether the wireless device is already a group owner in another group or a received signal strength of the first wireless device. IEEE 802.11 defines the PHY and medium access control (MAC) layers based on carrier-sense multiple access with collision avoidance (CSMA/CA). This

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1890-406: The wireless network. They transmit and receive radio frequencies for wireless-enabled devices to communicate with. Wireless clients can be mobile devices such as laptops, personal digital assistants , VoIP phones and other smartphones , or non-portable devices such as desktop computers , printers, and workstations that are equipped with a wireless network interface. The basic service set (BSS)

1935-488: Was able to reproduce these results using more advanced techniques. Nevertheless, RSSI does not always provide measurements that are sufficiently accurate to properly determine the location. However, RSSI still represents the most feasible indicator for localization purposes as it is available in almost all wireless nodes and it does not have any additional hardware requirements. For the most part, 802.11 RSSI has been replaced with received channel power indicator ( RCPI ). RCPI

1980-460: Was only used as an alternative to cabled LAN in places where cabling was difficult or impossible. Early development included industry-specific solutions and proprietary protocols, but at the end of the 1990s these were replaced by technical standards , primarily the various versions of IEEE 802.11 (in products using the Wi-Fi brand name). Beginning in 1991, a European alternative known as HiperLAN/1

2025-517: Was pursued by the European Telecommunications Standards Institute (ETSI) with a first version approved in 1996. This was followed by a HiperLAN/2 functional specification with ATM influences accomplished February 2000. Neither European standard achieved the commercial success of 802.11, although much of the work on HiperLAN/2 has survived in the physical specification ( PHY ) for IEEE 802.11a , which

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