Unilateration

Unilateration is a special breed of RTLS, i.e. locating or positioning systems. Unilateration is a special simplification applied to Real time locating as a technology to observe a process from any distance.
Cooperation
Objects or persons may support locating by cooperation or refrain from cooperation. In case there is no cooperation, the process of unilateration collapses to some type of detection. That term is referred in detail with respective technologies, as RADAR or SONAR and not subject of this page.
Principle and prerequisites
Concerning accuracy, especially numerical accuracy and accuracy of measurements, please refer to multilateration.
As the process of wireless communications for unilateration is a cooperative process, there must be two corresponding transmitters that are capable to initiate a session and to exchange information. The common approach despite RTLS is using fix mounted RFID readers with confinements or reader posts and mobile, passive RFID tags with objects. The more advanced approach i.e. with active RFID or RTLS or comparable systems delivers some more details about an event, as e.g.:
* identity of the instance
* distance towards the instance
* direction towards the instance
* speed of the instance
* orientation of the instance
* dimension of the spatial model
However, determining these details is not available without effort. All problems referred in the following may result from attempts top save effort. Other problems occur from complexity of the scenario neglecting what is in focus of the observer.
Orientation Problem
If unilateration is extended to the qualifying question for near or distant, a defined threshold between near and distant will be significant, whereas the threshold between distant and no contact may not be well defined.
If unilateration might be extended to deliver a scale and a measure for a distance, the problem remains, what such distance may describe, if no direction is included. Hence, by definition, orientation may be obtained by extending from unilateration to multilateration only.
Identification problem
The most common application is theft protection with low frequency RF tags (not RFID tags) that do not provide identity, but just serve detecting presence and thereby deliver evidence e.g. of unauthorized passing of a gate, instrumented as an electromagnetic bottleneck, where in short distance an RF tag is recognized and a loud or quiet anti-theft alarm is set.
Dilution of identity
As long as the individual that may become subject of locating will neither disclose its identity nor disclose its momentary location. some concepts of diluting precision (for locating) or randomizing data may (for identifying) be applied. Respective concepts shall be integrated to optimize acceptance with users.
Population problem
In case there are more than one object in the very same confinement, the answer yes is somewhat poor. Therefore the used components exchange identities, e.g. the moving object discloses its identity to the fix mount reader.
Addressing problem
In case an object is identified as an instance or individual in a dense population, this must correlate to ability of addressing the object for communicating. Such addressing is enabled e.g. via symbolic addresses, civic addresses or media addresses. Simple EAS systems just have an address length of 1 bit hence not prepared for discriminating instances.
Separation problem
The challenge is more complicated in case the communication percolates walls, the reply is even lesser determinated. Thus various hybrid concepts are in the market, where
* either the wireless communication is ultrasound based not to percolate walls
* or the wireless communication is infrared based not to percolate walls
* or the wireless electro-magnetic communication is in a low frequency range not to percolate walls
Ranging problem
Simple concepts just receive responses with the readers and assess the binary discrimination of success of interrogation or none. Higher sophisticated concepts receive signals and discriminate the power level of the received signal and assess these levels according to a propagation model converting level to distance.
Even higher sophisticated concepts map the distance information with an architectural model and allocate the response coming from an identified room. The most sophisticated concept try to map the distance information with an operational model and allocate the response coming from an identified work position. However, none of these approaches delivers a position, but simply matches with known symbolic locations.
More conceptual details may be found with respect to RADAR.
Direction problem
The ranging of broadcast does not deliver directions to single receivers. However, the propagation may be confined additionally by segmenting or sectoring the antennae patterns. This allows for some distinction of direction, but strictly limited to the partitioning of the antenna diagram. Commonly known solutions apply e.g. three sectors not just for directing the propagation, but to compensate for the fact that the antenna diagram otherwise might not cover a full circle.
None of these simple antennae pattern fragmentations addresses the problem of dynamic direction, i.e. the direction of motion.
More conceptual details may be found with respect to Sweeping.
Motion problem
None of the offered simpler system concepts in the market addresses the subject of motion nor the direction of motion. Normally the operational requirements cover just some approach to momentary location and no direct detection of motion or even direction of motion. To detect motion, as a differential of location, adequate sensing of such differentials is required. Single unilateral sensing does not serve this condition. However, the sequence of determined locations delivers a rough estimate of speed of lateral motion and hence a sufficient indication of direction of motion. Rotatory motion is per definition not addressed with unilateration.
More conceptual details may be found with respect to Doppler radar.
Model based sensing
The success for unilateration and as well for multilateration demands proper modelling of the operational requirements. For details on such, the locating engine concept and the real time locating systems approaches delivers basing methodology. Unilateration shall be understood as a cheap and easy approach to provide evidence on presence and distance. Multilateration however shall be understood as a comprehensive approach to provide information beyond with location and possibly orientation of an object.
Dimensions of detecting and ranging
Unilateration provides of distance per measuring unit. As far as measuring a distance is included, the result is graded with distance. Implication of a priori knowledge improves the obtained information.
As directing of the measuring beam is not included and as far as locations of the measured targets are not available, unilateration principally cannot deliver a plan view in two dimensions, let alone in three dimensions, from measuring. Hence multilateration is required.
Dimension of the model
Communicating the technically elaborated details about a relation between the observer and the observed object requires some distinction of visualizing. The most common displays are flat, hence the model of visualization mostly is a 2D model. 3D representation may be achieved by separating two angular views or by presenting a foreshortened view, which then allows for better situation assessment, but hampers a visual quantifying approach depending on the chosen aspect.
However, modeling a spatial process in 2D only and before projecting the result to a flat display, causes improper reduction of information down to unintelligibility. The better approach is to hide the complexity of reality to the observer, but compute the scenario in a 3D model implying a priori knowledge and then simplify the image to an operationally sound 2D display.
Verify presence
Presence of an object shall be verified before further attempts of lateration, trilateration or multilateration. The detection of an object is the first step. In cooperative processes there must be some response from the object to establish a communications session for further information exchange.
Verification may start without delay after detection. However, cooperation generally requires establishment of a respective session for information exchange with both partners.
Verify presence by signature
This basically is the most crude option, when an object or a person will not cooperate. In case of any reflection, scattering or radiation of energy, a received signature of the target may be compared by the receiver with known characteristic patterns and then inferred with knowledge about possibility of appearance. This option normally is applied under operational conditions that may be reserved to state power entities, as any type of police or military.
The term signature however applies as well to secured verification principles. This however describes a cooperative process of assessment and comparison, which generally is understood as a second step after disclosing an asserted identity.
Verify presence by identity
The first step in cooperation after detecting is the cooperative confirmation of identity. This may be somewhat restricted. i.e. limited to group identity, or more definite with identity of the instance. The class of identity may be some address, i.e. the media address (MAC address) or any other address, i.e. email address, mail address or other representation of a communications link. However such identification does not disclose location.
Verify presence by civic location
A sound approach to verification for all types of communications is the cooperative disclosure of a civic address, which combines the identity of an instance with a location, where this instance is residing or just registered. Such disclosure enables symbolic locating, where the civic location describes a certain place in a community. However such verification is a nominal type to prove registration and not a proof for actual presence. Such addressing is specified in detail with IETF RFC 4119 and the successor RFC 5139 . However, civic location does not provide generally a resolution down to single rooms.
Verify presence in confinements
The operational task is to verify e.g. a tagged object is on an area or in a room and to read its identity. Opposite result may be no tagged object is on that area or no tagged object is in the room. This is enabled with activating a mobile tag with a frequency confined in propagation to that single room and a second frequency communicating the response possibly to receivers nearby, not necessarily in that room. Then loading the activation with a room identity, the response may refer to the very same room identity without limiting the range of response to the very same room.
Verify passage at borderlines
A good service as described is the theft protection. This application is served with tags that either work or get destroyed by the cashier after paying.
A better service is the asset protection, where alarms are restricted to unauthorized carriage. The concept is comparable to theft protection, but includes identifying the object carried. However, it would be a nuisance to hear a loud alarm bringing the object into the confinement. Even to discriminate the direction of passage, unilateration must be enriched with
* either double gating determining a sequence of passages,
* or several steps of gating with sufficient density to establish a track,
* or a single gating determining a direction of passage with angulation.
The latter alternative, however, is per definition beyond lateration.
Applications of unilateration
Unilateration is widely spread as a technology to obtain information in real-time from process observation. However, the low degree of abstraction to this term prevents from comparison of technologies with similar RFID and sophisticated RTLS on one hand and with different approaches as Closed-circuit television on the other hand.
Electronic Article Surveillance
The most common application is with Electronic Article Surveillance (EAS) to counter shoplifting. There at a narrow gate a special detector detects a target by means of a transponder at frequencies e.g. of 4.6 MHz, 8.2 MHz etc .
The more advanced system shall favourably discriminate the direction of motion to prevent from alarms on objects moving into the shop as well as keeping quiet for targets moving outside a dual antennae gate. More skilled solutions may discriminate also on distance, hence providing real unilateration.
Tracking of individuals
Another common application is tracking of handicapped persons, e.g. people with dementia or Alzheimer's disease. In gerontology care units, care stations for elderly people and especially with demented people, the uncontrolled and unregistered disappearance of clients is a severe hazard for the patient himself as well as for the care unit as an insurance risk and a practical problem for the cartaking staff of the elderly.
The very economized systems rely on active hybrid tags with IR receivers and ultrasound or RF beacons as well as on room detectors and further detectors at bottlenecks in aisles and alleys, gates and entrances, as e.g. the systems from SONITOR and RF Code .
The other approach with WLAN based systems suggests higher qualification, as e,g, the systems from EKAHAU , but may easily fail, as soon as the ambient transmission environment changes, affects the recorded propagation mapping and leads in the best case to just the very same quality of results as with RF beacons.
In both cases the basic principle is again cooperation: The person to be detected and found must be equipped before the disappearance happens. Therefore especially for elderly people the beacon unit must be hidden from its original purpose to prevent the aged person to throw it away as an unnecessary burden, or just an ugly trinket, when not observed.
Anti-collision in warehouses
Conventional warehousing using forklifts provides all degrees for freedom for positioning goods. As well forklifts are a universal threat to persons working in warehouses. Collision is a common risk, however, accident prevention with the training concepts of employers mutual insurance association focuses on auto-exposure to accident risk.
The heavier accidents occur when colliding with walkers: The misbalance of dead weight causes severe damage to walkers more than to drivers.
Anti-collision warning based on unilateration is a sound approach. The basic principle with unilateration is again a cooperative one: Any target in reach is detected on approach. Warning is sent to driver as well as to walker by buzzers, vibrators and flashers. Alertness is rapidly improved beyond just visualization.
Emergency search rescue
A major application of unilateration concept is unsing a so-called Distress radiobeacon with traditional approaches for the search and rescuing of people from sea faring, mountain climbing, desert disorientation and other accidents with avalanches, earthquakes or landslips e.g. with satellite assistance , especially according to the EPIRB standards .
The basic principle with unilateration is again a cooperative one: The person to be rescued must be equipped before the accident happens. The quality and quantity of detecting systems is vast and various, even since common availability of GPS services. The simple radio-frequent beacons still serve as a means to find persons drifting in the seas or lying under masses of snow or soil .

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