LBS Location Based Services

A Location-Based Service (LBS) is an information or entertainment service, accessible with mobile devices through the mobile network and utilizing the ability to make use of the geographical position of the mobile device ^{[1] [2] [3]} .^[4]
LBS can be used in a variety of contexts, such as health, indoor object search^[5], entertainment^[6], work, personal life, etc. .^[7]
LBS include services to identify a location of a person or object, such as discovering the nearest banking cash machine or the whereabouts of a friend or employee. LBS include parcel tracking and vehicle tracking services. LBS can include mobile commerce when taking the form of coupons or advertising directed at customers based on their current location. They include personalized weather services and even location-based games. They are an example of telecommunication convergence.
This concept of location based systems is not compliant with the standardized concept of real-time locating systems and related local services (RTLS), as noted in ISO/IEC 19762-5 ^[8] and ISO/IEC 24730-1.^[9]

History

Research forerunners of today's location-based services are the infrared Active Badge system (1989–1993), The Ericsson-Europolitan GSM LBS trial ran during 1995 by Jörgen Johansson and the master thesis written by Nokia employee Timo Rantalainen, in 1994.
In 1996 the US Federal Communication Commission (FCC) issued rules requiring all US mobile operators to locate emergency callers. This rule was a compromise resulting from US mobile operators seeking the support of the emergency community in order to obtain the same protection from law suits relating to emergency calls as fixed-line operators already had.
In 1997 Christopher Kingdon, of Ericsson, handed in the Location Services (LCS) stage 1 description to the joint GSM group of the European Telecommunications Standard Institute(ETSI) and the American National Standards Institute (ANSI). As a result the LCS sub-working group was created under ANSI T1P1.5. This group went on to select positioning methods and standardize Location Services (LCS), later known as Location Based Services (LBS). Nodes defined include the Gateway Mobile Location Centre (GMLC), the Serving Mobile Location Centre (SMLC) and concepts such as Mobile Originating Location Request (MO-LR), Network Induced Location Request (NI-LR) and Mobile Terminating Location Request (MT-LR).
In 2000, after approval from the worlds 12 largest telecom operators, Ericsson, Motorola and Nokia jointly formed and launched the Location Interoperability Forum Ltd (LIF). This forum first specified the Mobile Location Protocol (MLP), an interface between the telecom network and an LBS application running on a server in the Internet Domain. Then, much driven by the Vodafone group, LIF went on to specify the Location Enabling Server (LES), a "middleware", which simplifies the integration of multiple LBS with an operators infrastructure. In 2004 LIF was merged with the Open Mobile Association (OMA). A LBS work group was formed within the OMA.
The first consumer LBS-capable mobile web device was the Palm VII, released in 1999.^[10] Two of the in-the-box applications made use of the ZIP code-level positioning information and share the title for first consumer LBS application: the Weather.com app from The Weather Channel, and the^[11] TrafficTouch app from Sony-Etak / Metro Traffic.
The first LBS services were launched during 2000 by TeliaSonera in Sweden (friendfinder, yellow pages, houseposition, emergency call location etc.) and by EMT in Estonia (emergency call location, friend finder, TV game). TeliaSonera and EMT based their services on the Ericsson Mobile Positioning System (MPS).
Other early LBS include friendzone, launched by swisscom in Switzerland in May 2001, using the technology of valis ltd. The service included friend finder, LBS dating and LBS games.^[12] The same service was launched later by Vodafone Germany, Orange Portugal and Pelephone in Israel^[11]. Microsoft's Wi-Fi-based indoor location system RADAR (2000), MIT's Cricket project using ultrasound location (2000) and Intel's Place Lab with wide-area location (2003).^[13]
The first commercial LBS service in Japan was launched by DoCoMo, based on triangulation for pre-GPS handsets in July 2001, and by KDDI for the first mobile phones equipped with GPS in December 2001.^[14] Mobile handset makers have tended to take 'upstream initiative' to embed LBS in their mobile equipment. Originally, LBS was developed by mobile carriers in partnership with mobile content providers.
In May 2002, go2 and AT&T launched the first (US) mobile LBS local search application that used Automatic Location Identification (ALI) technologies mandated by the FCC. go2 users were able to use AT&T’s ALI to determine their location and search near that location to obtain a list of requested locations (stores, restaurants, etc.) ranked by proximity to the ALI provide by the AT&T wireless network. The ALI determined location was also used as a starting point for turn-by-turn directions.
The main advantage is that mobile users don't have to manually specify ZIP codes or other location identifiers to use LBS, when they roam into a different location. GPS tracking is a major enabling ingredient, utilizing access to mobile web.
In 2010, location-based services power Mobile Local Search to enable the search and discovery of persons, places, and things within an identifiable space defined by distinct parameters. These parameters are evolving. Today^[when?] they include social networks, individuals, cities, neighborhoods, landmarks, and actions that are relevant to the searcher's past, current, and future location. These parameters provide structure to vertically deep and horizontally broad data categories that can stand alone or are combined to form searchable directories.^[15]

Locating methods

Control Plane Locating

Sometimes referred to as positioning, with control plane locating the service provider gets the location based on the radio signal delay of the closest cell-phone towers (for phones without GPS features) which can be quite slow as it uses the 'voice control' channel.^[4] In the UK, networks do not use trilateration; LBS services use a single base station, with a 'radius' of inaccuracy, to determine a phone's location. This technique was the basis of the E-911 mandate and is still used to locate cellphones as a safety measure. Newer phones and PDAs typically have an integrated A-GPS chip.
In order to provide a successful LBS technology the following factors must be met:

• Coordinates accuracy requirements that are determined by the relevant service;
• Lowest possible cost;
• Minimal impact on network and equipment.

Several categories of methods can be used to find the location of the subscriber.^[2][16] The simple and standard solution is GPS-based LBS. Sony Ericsson's "NearMe" is one such example. It is used to maintain knowledge of the exact location, however can be expensive for the end-user, as they would have to invest in a GPS-equipped handset. GPS is based on the concept of trilateration, a basic geometric principle that allows finding one location if one knows its distance from other, already known locations.

GSM Localization

GSM localization is the second option. Finding the location of a mobile device in relation to its cell site is another way to find out the location of an object or a person. It relies on various means of multilateration of the signal from cell sites serving a mobile phone. The geographical position of the device is found out through various techniques like time difference of arrival (TDOA) or Enhanced Observed Time Difference (E-OTD).

Others

Another example is Near LBS (NLBS), in which local-range technologies such as Bluetooth, WLAN, infrared and/or RFID/Near Field Communication technologies are used to match devices to nearby services. This application allows a person to access information based on their surroundings; especially suitable for using inside closed premises, restricted/ regional areas.
Another alternative is an operator- and GPS-independent location service based on access into the deep level telecoms network (SS7). This solution enables accurate and quick determination of geographical coordinates of mobile phone numbers by providing operator-independent location data and works also for handsets that are not GPS-enabled.
Many other Local Positioning Systems are available, especially for indoor use. GPS and GSM don't work very well indoors, so other techniques are used, including Bluetooth, UWB, RFID and Wi-Fi^[17]. But which technique provides the best solution for a specific LBS problem? A general model for this problem has been constructed at the Radboud University of Nijmegen.^[18]

Further information: Mobile phone tracking

LBS applications

Some examples of location-based services are ^[2]:

• Recommending social events in a city^[1]
• Requesting the nearest business or service, such as an ATM or restaurant
• Turn by turn navigation to any address
• Locating people on a map displayed on the mobile phone
• Receiving alerts, such as notification of a sale on gas or warning of a traffic jam
• Location-based mobile advertising
• Asset recovery combined with active RF to find, for example, stolen assets in containers where GPS wouldn't work
• Games where your location is part of the game play, for example your movements during your day make your avatar move in the game or your position unlocks content.
• Real-time Q&A revolving around restaurants, services, and other venues

More examples are listed in.^[2]
For the carrier, location-based services provide added value by enabling services such as:

• Resource tracking with dynamic distribution. Taxis, service people, rental equipment, doctors, fleet scheduling.
• Resource tracking. Objects without privacy controls, using passive sensors or RF tags, such as packages and train boxcars.
• Finding someone or something. Person by skill (doctor), business directory, navigation, weather, traffic, room schedules, stolen phone, emergency calls.
• Proximity-based notification (push or pull). Targeted advertising, buddy list, common profile matching (dating), automatic airport check-in.
• Proximity-based actuation (push or pull). Payment based upon proximity (EZ pass, toll watch).

In the U.S. the FCC requires that all carriers meet certain criteria for supporting location-based services (FCC 94-102). The mandate requires 95% of handsets to resolve within 300 meters for network-based tracking (e.g. triangulation) and 150 meters for handset-based tracking (e.g. GPS). This can be especially useful when dialing an emergency telephone number - such as enhanced 9-1-1 in North America, or 112 in Europe - so that the operator can dispatch emergency services such as Emergency Medical Services, police or firefighters to the correct location. CDMA and iDEN operators have chosen to use GPS location technology for locating emergency callers. This led to rapidly increasing penetration of GPS in iDEN and CDMA handsets in North America and other parts of the world where CDMA is widely deployed. Even though no such rules are yet in place in Japan or in Europe the number of GPS-enabled GSM/WCDMA handset models is growing fast. According to the independent wireless analyst firm Berg Insight the attach rate for GPS is growing rapidly in GSM/WCDMA handsets, from less than 8 percent in 2008 to 15 percent in 2009.^[19]
European operators are mainly using Cell-ID for locating subscribers. This is also a method used in Europe by companies such as Podsystem that are using cell based LBS as part of systems to recover stolen assets. In the US companies such as Rave Wireless in New York are using GPS and triangulation to enable college students to notify campus police when they are in trouble. Rave Wireless and other companies with location based offerings are powered by a variety of companies, including Skyhook Wireless and Xtify.

Mobile messaging

Mobile messaging plays an essential role in LBS. Messaging, especially SMS, has been used in combination with various LBS applications, such as location-based mobile advertising. SMS is still the main technology carrying mobile advertising / marketing campaigns to mobile phones. A classic example of LBS applications using SMS is the delivery of mobile coupons or discounts to mobile subscribers who are near to advertising restaurants, cafes, movie theatres. The Singaporean mobile operator MobileOne carried out such an initiative in 2007 that involved many local marketers, what was reported to be a huge success in terms of subscriber acceptance.
Companies offering location-based messaging (sometimes referred to as 'geo-messaging') include The Coupons App [1](US), Centrl [2](International), Zhiing (international), BluePont (US),^[20] Loopt (US), Dodgeball (US) and GeoMe [3](Spain).

Privacy issues

With the passing of the Can Spam Act in 2005, it became illegal in the United States to send any message to the end user without the end user specifically opting-in. This put an additional challenge on LBS applications as far as 'carrier-centric' services were concerned. As a result, there has been a focus on user-centric location-based services and applications which give the user control of the experience, typically by opting in first via a website or mobile interface (such as SMS, mobile Web, and Java/BREW applications).
The European Union also provides a legal framework for data protection that may be applied for location-based services, and more particularly several European directives such as: (1) Personal data: Directive 95/46/EC); (2) Personal data in electronic communications: Directive 2002/58/EC; (3) Data Retention: Directive 2006/24/EC. However the applicability of legal provisions to varying forms of LBS and of processing location data is unclear.^[21]
One implication of this technology is that data about a subscriber's location and historical movements is owned and controlled by the network operators, including mobile carriers and mobile content providers.^[22]
A critical article by Dobson and Fisher^[23] discusses the possibilities for misuse of location information.
Beside the legal framework there exist several technical approaches to protect privacy using privacy-enhancing technologies (PETs). Such PETs range from simplistic on/off switches ^[24] to sophisticated PETs using anonymization techniques,^[25] e.g., related to k-anonymity. Today, only few LBS offer such PETs, e.g., Google Latitude offers an on/off switch and allows to stick one's position to a free definable location. Additionally, it is an open question how users perceive and trust in different PETs. The only study that addresses user perception of state of the art PETs is.^[26]. Another set of techniques included in the PETs are the Location obfuscation techniques, which slightly alter the location of the users in order to hide their real location while still bein able to represent their position and receive services from their LBS provider.

RTLS Real Time Locating Systems

Real-time locating systems (RTLS) are a type of local positioning system that allow to track and identify the location of objects in real time. Using simple, inexpensive badges or tags attached to the objects, readers receive wireless signals from these tags to determine their locations.^[1] RTLS typically refers to systems that provide passive or active (automatic) collection of location information.
Location information usually does not include speed, direction, or spatial orientation. These additional measurements would be part of a navigation, maneuvering or positioning system.

Origin

The term RTLS was created (circa 1998) to describe an emerging technology that not only provided the Automatic Identification capabilities of active RFID tags, but added the ability to see the physical location of the tagged asset on a computer screen. Although this capability had been utilized previously by military and government agencies, the technology had been too expensive for commercial purposes.
By the early 1990's, commercialization began at two healthcare facilities in the United States (Foote Hospital in Jackson, MI and Broward Children's Hospital in Pompano Beach, FL). These early adoptors are atrributed to real-time locating industry innovator Precision Tracking (Versus Technology, Inc.) and were based on the transmission and decoding of infrared light signals from actively transmitting tags.

System designs

RTLS excludes passive RFID indexing (radio frequency transponder indexers) and Cellnet base station segment locators (location-based services) from the scope of the ISO/IEC approach to RTLS standardization as well as all beacon systems, that ping without request. RTLS systems apply typically in confined areas, where the required reference points would be equipped with wireless anchor nodes.

Operation

For RTLS to function, the location of tagged items must be determined either by a central processor or by an embedded mobile computing facility. Locating is generally accomplished in one of the following ways

• 1. ID signals from nodes are identifiable to a single reader in a sensory network thus indicating the coincidence of reader and nodes.
• 2. ID signals from nodes are picked up by a multiplicity of readers in a sensory network and a position is estimated using one or more locating algorithms
• 3. Location signals from signposts with identifiers are transmitted to the moving nodes and are then relayed, usually via a second wireless channel, to a location processor.
• 4. Mobile nodes communicate with each other and perform metering distances.

Examples one (1) and three (3) have much of the same characteristics. They typically require that a node be assigned at a time to a single reader/signpost. Separation from overlapping readers/signposts is roughly provided by RSSI or Physical Space Division (walls/floors/ceilings). Readers/signposts are often associated with highly stable location boundaries (i.e. a room or room division). In these examples, locations are listed as "Current Location" or "Last Known Location."
Example two (2) requires that distances between nodes in the sensory network be determined in order to precisely locate a node. In this instance, the determination of the location is called Localization. The location is calculated through Trilateration or Multilateration from the determined distance between the nodes or through Triangulation from the determined angles between nodes. The determination of distances is called Ranging.

Application

RTLS serves in operational areas for logistics and other services,as for example stock grounds or storehouses, and for servicing areas in clinics and industrial plants. Tasks done by a RTLS include:

• to combine identity and location of any type of items or objects
• to combine identity of items with location of lifter placing the items
• to ensure permanent availability of proper information about temporary placement
• to support notification of placing of items
• to prove proper manning of operational areas
• to prove consequent evacuation of endangered areas
• to make marshalling staff dispensable

Standards

ISO/IEC

The basic issues of RTLS are standardized by the International Organization for Standardization and the International Electrotechnical Commission, under the ISO/IEC 24730 series. In this series of standards, the basic standard ISO/IEC 24730-1 identifies the terms describing a form of RTLS used by a set of vendors, but does not encompass the full scope of RTLS technology.
Currently several standards are published or under discussion:

• ISO/IEC FDIS 19762-5 Information technology AIDC techniques — Harmonized vocabulary, Part 5 — Locating systems
• ISO/IEC 24730-1:2006 Information technology real-time locating systems (RTLS) Part 1: Application program interface (published).
• ISO/IEC 24730-2:2006 Information technology real-time locating systems (RTLS) Part 2: 2,4 GHz Air interface protocol (published, WhereNet/Zebra approach).
• ISO/IEC WD 24730-5 Information technology real-time locating systems (RTLS) Part 5: (drafted ISO/IEC standard out for balloting in 2008, Nanotron approach).

The other proposals ISO/IEC 24730-3 and ISO/IEC 24730-4 had never left the stage of intention. For copies of these documents see references.
These standards do not stipulate any special method of computing locations, nor the method of measuring locations. This may be defined in specifications for triangulation or any hybrid approaches to trigonometric computing for planar or spherical models of a terrestrial area.

ANSI standards

• ANS/INCITS 371: Information Technology – Real-Time Locating Systems (RTLS).

Ranging

Ranging, as a special term for measuring distance, is the prerequisite for locating. Measuring a bearing angle, i.e. angulating is the other alternative.
Determining the distance may be either a non cooperative scanning process, as with RADAR or LIDAR, or a cooperative direct distance measuring process, as with RTLS. A scanned beam may form an overall image as a model of the whole scene. In all other cases the image of the scene is rather selective.
The following step is extracting the distance information from the scanned image. Direct distance measurement with a single beam targets only the object to be measured, for example, with a laser. This method requires additional information about the direction of the beam. The remaining method is omni-directional transmission with a signal containing an address code. Only the addressed object responds to the request. The time required for the signal to reach the object can be used to calculate the distance. After completing the distance measurement, the location may be computed.
There are two different principles when measuring travel time of radio waves:

• Trilateration derives the travel time of a radio signal from a metering unit, and measures and computes the distance with the relation of light speed in vacuum, the (Time of arrival concept).

• Triangulation derives the travel time of a pair of synchronous radio signals from a metering unit with two transmitters, and measures and computes the difference of distance with the relation of light speed in vacuum as an angle versus the baseline of the two transmitters (TDOA time difference of arrival concept).

All the terms named here just apply to measurement concepts. All information about location is for services applied to mobile or portable or otherwise transportable objects. Location information may be relevant for managing interaction of persons with services as well.

• Angle of arrival (AoA)
• Line-of-sight (LoS)
• Time of arrival (ToA)
• Multilateration (Time difference of arrival) (TDoA)
• Time-of-flight (ToF)
• Two-way ranging (TWR) according to Nanotron’s patents
• Symmetrical Double Sided – Two Way Ranging (SDS-TWR)
• Near-field electromagnetic ranging (NFER)

Privacy concerns

RTLS may be seen a threat to privacy, if applied to persons, either directly or parasitically. The requirement therefore is to describe the purpose and the conditions of operation to those affected and to advertise for expressed agreement. Recent adjustment of jurisdiction leads to more careful assessment of needs and options. The newly declared human right of informational self-determination de:Informationelle Selbstbestimmung, i.e. to prevent one's identity and personal data from disclosure to others, covers disclosure of locality as well. Base of discussion is very similar to disclosure of personal data for passing immigration at US airports: Balancing threat and burden [4].

Types of technologies used

There is a wide variety of systems concepts and designs to provide real-time locating. A good choice is listed in RTLS for Dummies by Ajay Malik (Wiley 2009).^[2] Methods include:

• Active radio frequency identification (Active RFID)
• Active radio frequency identification - infrared hybrid (Active RFID-IR)
• Infrared (IR)
• Optical locating,^[3][4]
• Low-frequency signpost identification
• Semi-active radio frequency identification (semi-active RFID)
• Radio beacon,^[5][6]
• Ultrasound Identification (US-ID) ^[7]
• Ultrasonic ranging (US-RTLS) ^[8]
• Ultra-wideband (UWB) ^[9]
• Wide-over-narrow band ^[10]
• Wireless Local Area Network (WLAN, Wi-Fi)^[11]
• Bluetooth,^[12][13]
• Clustering in noisy ambience,^[14][15]
• Bivalent systems ^[16]

A general model for selection of the best solution for a locating problem has been constructed at the Radboud University of Nijmegen.^[17] Many of these references do not comply with the definitions given in international standardization with ISO/IEC 19762-5 ^[18] and ISO/IEC 24730-1.^[19] However, some aspects of real-time performance are served and aspects of locating are addressed in context of absolute coordinates.

Locations for sensors

Locating at choke points

There is class of most simple locating which applies no physical measurement at all, but just communicates at coincidence of transceiver and transponder. Then locating collapses to simple application of RFID technologies according to the equivalent standard.^[20] This is the only option to apply passive RFID tags for locating. Then the reach of the RFID reader determines the choke point. Hence accuracy is defined by the sphere spanned with the reach of the reader.

Locating in relative coordinates

Many references describe locating a relative coordinates. This is a valuable support for many operational needs, whereas the precision of the term RTLS is widely diluted to arbitrary interpretation. Such solutions may be referred as fuzzy locating.

Locating in absolute coordinates

The high precision of satellite navigation systems led to some snugness in setting the requirements for locating of objects. generally the determining of absolute coordinates is the most challenging approach. Such solutions may be referred as crisp locating.The difference to the qualities of relative coordinates may be easily sensed with indoor operations, where satellites are not commonly available for referring to global coordinates.

Locating in contiguity

A newer approach for locating defines a location just as the contiguous ambience of the person looking for something to be located. That is very similar to choke point locating, However, the accuracy may be much better tuned, as the reach is not influenced by the illumination of the tag with the reader, but just by the transmission power level of the active RFID tag as a beacon.
This is the easy option to apply active RFID tags for economised locating. Then the reach of the RFID receiver determines the base point. Hence accuracy is defined by the algorithm for varying the minimum reach of transmission of the beacon. Solutions ara available as very simple electronic leashes or in more complex designs.

Erratic effects in locating systems

Real-time locating is affected by a variety of errors. The major reasons are physical and may not be reduced by improving the technical equipment. The only escape is mathematical intelligence to improve.

None or no direct response

Many RTLS systems have a very mundane requirement: they require direct and clear wireless visibility. For those systems, where there is no visibility on the path from mobile tags to resident nodes there will be no result or a non valid result from locating engine. This applies to satellite locating as well as other RTLS systems such as angle of arrival and time of arrival. Fingerprinting is a way to overcome the visibility issue: If the locations in the tracking area contain distinct measurement fingerprints, line of sight is not necessarily needed. For example, if each location contains a unique combination of signal strength readings from transmitters, the location system will function properly. This is true, for example, with some Wi-Fi based RTLS solutions. However, having distinct signal strength fingerprints in each location typically requires a fairly high saturation of transmitters.

False location

The measured location may appear entirely faulty. This is a generally result of simple operational models to compensate for the plurality of error sources. It proves impossible to serve proper location after ignoring the errors.

Locating backlog

Real time is no registered branding and has no inherent quality. A variety of offers sails under this term. As motion causes location changes, inevitably the latency time to compute a new location may be dominant with regard to motion. Either an RTLS system that requires waiting for new results is not worth the money or the operational concept that asks for faster location updates does not comply with the chosen systems approach.

Temporary location error

Location will never be reported exactly, as the term real-time and the term precision directly contradict in aspects of measurement theory as well as the term precision and the term cost contradict in aspects of economy. That is no exclusion of precision, but the limitations with higher speed are inevitable.

Steady location error

Recognizing a reported location steadily apart from physical presence generally indicates the problem of insufficient over-determination and missing of visibility along at least one link from resident anchors to mobile transponders. Such effect is caused also by insufficient concepts to compensate for calibration needs.

Location jitter

Noise from various sources has an erratic influence on stability of results. The aim to provide a steady appearance increases the latency contradicting to real time requirements.

Location jump

As objects containing mass have limitations to jump, such effects are mostly beyond physical reality. Jumps of reported location not visible with the object itself generally indicate improper modeling with the location engine. Such effect is caused by changing dominance of various secondary responses.

Location creep

Location of residing objects gets reported moving, as soon as the measures taken are biased by secondary path reflections with increasing weight over time. Such effect is caused by simple averaging and the effect indicates insufficient discrimination of first echoes.

Fuzzy Tracking and Locating System

Fuzzy locating is a rough but reliable method based on appropriate measuring technology for estimating a location of an object. The concept of precise or ‘’crisp locating’’ is replaced with respect to the operational requirements and the economic viability. In most cases the knowledge of exact coordinates does not contribute to operations, but the spatial or planar relation between entities is relevant. Hence fuzzy locating determines the radial distances between entities involved in an operational process and reduces the required accuracy of measurement to basic qualities of close, near or far and to relations simple as in or out. However such segregation shall be achieved with high reliability and sound repetition.

Basics

The term fuzzy relates to rough spatial coincidence or contiguity assessment compared to the alternative crisp locating, which derives precise coordinates of a location of an object. The fuzzy part of the locating process balances the physical and the mathematical portions of processing measurement data of the objects involved and a priori knowledge with the operational ambience.
The result of fuzzy locating shall suffice for operational support and not for metric confirmation of measures taken at earlier occasions. However, available information is exploited as a priori knowledge. Fuzzy locating compares with the distinction respectively segregation of mathematical logic with the terms crisp sets and crisp relations or fuzzy sets and fuzzy relations.
Systematic and stochastic errors occurring under operational requirements and conditions turn virtually precise measures in a friendly ambience to fuzzy metrics. In even worse ambient conditions, which mostly applies to wireless propagation in ISM bands this leads to erratic results and various misinterpretation. In consequence the trade off between technical effort and achieved operational support adjusts inevitably to physical limitations as well as to weaknesses in mathematical modeling. Better resolved balancing deliberately neglects classical terms of precision in favour of a strong commitment for operational unambiguity.

The techno-economic challenge

Generally precision is obtained at expense. The balancing of capital expenditure and of operational cost shall take into account not what is possible, but what is necessary. A better designed balancing leads to the less precise fuzzy locating at much lesser expense: As a more general approach, fuzzy locating is a method for best estimating a roughly determined location of an object as a distinction of operational contiguity. Contiguity means more or less a handy distance between an individual and an object. Three basic situations generally apply:

• Basic task is for example current presence in a room, well discriminated from other adjacent rooms.
• The more challenging requirement is to segregate the presence of an object or an individual at just one of several work positions in the very same room or with any other known and well referred place on this room.
• The more generalized approach hence is the spatial relationship between an object and an individual in any ambience, defining the actual location of either the object or alternatively the individual as the point of reference.

In all three cases the absolute coordinates are not of interest, as long as the discrimination of rooms or work positions is reliably achieved.

Wireless, optical and acoustical approaches

For the locating task an object to be located must be at least equipped with a wireless tag in a wireless communication environment. Each operating wireless target in a wireless communication environment may contribute. Prerequisite for radio frequency based wireless cooperation is some cohesion of the wireless nodes in a networking concept. Each wireless target has at least one physical propagation parameter that varies with location. Better qualified approaches make use of more than one physical parameter.
Alternatively optical and acoustical solutions are known. Variation of parameters is partly deterministic with varying distances between wireless nodes. A location estimate approximating the real location of the transmitter preferably under real time constraints is determined on the basis of a stochastical model of propagation and a model for the process of observation in a noisy ambience and on a chosen set of observed deterministic parameters of transmission and propagation.

Implemented examples

Several suppliers offer the so-called electronic leash solution. This serves for wirelessly tethering mobile appliances with each other. The RSSI estimate serves for a radial metrics, but without any certified calibration. Setting an alam on unintentional loss is the key servcice offered with this concept. An advanced aspect has been launched with Bluetooth low energy for better economised battery life cycle. Special trimming serves for two years operation from a button cell^[1].

Comparison to metric locating

Metric or crisp locating determines a spatial or planar relationship between independently moving or residing entities (usually addressed as targets) by means of qualified methods for measuring distances. This is the topic for example of

• satellite positioning systems, as GPS or Galileo or
• real time locating systems (RTLS) as defined with ISO/IEC 19762-5 or
• inertial navigation systems (INS)

These technologies generally make use of a travel time measurement as the approach with best resolution and precision. Further enhancement is achieved with time differences discriminated for severalpaths. Such basic or enhanced travel time measurement requires a multiplicity of measures for unambiguous locating.
All of these sophisticated physical methods of measuring are hampered with a challenge caused by motion and caused by transmitter population. This makes restrictions effective in time both for observation and capture and for communication of measurement data. In consequence, the pecuniary and the technical effort adjusts to physical limitations and the limited metric precision with a special aspect to operational clarity. Such balancing neglects classical terms of metric precision, prevents from over-interpreting erratic measures and provides sufficient escape.
Additionally the model of propagation contributes to the achieved results. In satellite based systems generally direct line of sight is generally required, without escape. That determines the restriction with applying such approach between buildings or, even worse, inside buildings: The highest precision does not compensate for bad visibility. Whenever the path of propagation gets cranked, the result of time measurement gets biased.
In comparison to locating on the move, exactly determining a location with highest possible precision is the topic of geodesy and surveying. These disciplines traditionally do not deal with motion and may integrate over long time. The terms of 'locating', 'positioning' and 'navigating' or 'surveying' are commonly used in almost equivalence, hence neglecting that the sense of these terms is different concerning sensor and actor functions and motion conditions.

Radio signal strength indication (RSSI) as a coarse metrics

For many purposes, a distinct and reliable determination of a location relative to somewhat rastered position on a floor or just a room in a building will be sufficient for sound fuzzy locating by single measurements.
Typically fuzzy locating coincides with simple power level measurement, usually configured as unilateration. A combination of multiple distance measurement, as a multilateration, based on power level measurement, appears unbalanced. The effort for multiple measures aiming at an unambiguous multilateration process will not be justified with the achievable precision of the results of power level measures.
Though leaving some ambiguity with sparse measurements, the contiguity may be assessed applying a priori knowledge. Such includes primarily tracking motion over time. As a generalized approach the fuzzy locating based on power levels measured with wireless nodes will roughly suffice for coarse guessing a location, where an object or a person with a wireless node resides in contiguity to other wireless nodes in a wireless environment.
Therefore each wireless node recognises the received power level with the distance to the transmitting wireless node and this parameter can be measured. Some additional calibration parameters serve as a basis for the statistical model of the parameters of propagation in a known neighborhood of distributed wireless nodes and of other passive objects, which influence propagation. A location estimate, which approximates the approach of the transmitting node, will be described with the stochastic model of propagation and the statistics of the monitored parameters.

Offered discrimination of positions

For applications where no need for absolute coordinates determination is assessed, the implementing of a more simple solution is advantageous. Compared to multilateration as the concept of crisp locating, the other option is fuzzy locating, where just one distance delivers the relation between detector and detected object. This most simple approach is unilateration. However, such unilateration approach never delivers the angular position with reference to the detector. Many solutions are available today ^{[2][3][4][5][6]}.
Some of these vendors offer a position estimate based on combining several laterations (Ekahau, ZOMOFI). This approach may often appear instable, when the wireless ambience is regularly affected by moving or re-positioning of metal objects or water masses. Other vendors offer room discrimination with a room-wise excitation, one vendor offers a position discrimination with a contiguity excitation.

Offered qualities with auxiliary mapping

Increasing accuracy means increasing cost. The most indirect approach is the increase of distributed anchor nodes (Ekahau). The first direct approach simply is a fixed excitation through wall-mounted wireless nodes or optical excitors. That will provide a sound room discrimination in any case (Sonitor, RF Code, TokLoc). The second direct approach is the position discrimination using apparently available infrastructure objects, as with networked work stations yet equipped with Bluetooth transponders (TokLoc).
The easy escape beyond increase of accuracy in measuring is the accuracy gain with mapping. Such mapping seldom suffices when performed statically. The more advantageous approach is a combination of initial mapping based on floor plans or area maps with an intelligent update based on updates obtained from actual measuring. That is offered with the concept of simultaneous Locating and Mapping ^[7].

Physical restrictions

Measurement of propagation parameters is generally heavily loaded with various noise components. Such noise may be stochastic ([white noise]) or deterministic or a mixture of noises with limited bandwidth ([pink noise]).
As with all wireless systems, qualities of measurement in any one aspect contradict to qualities in some other aspects:

• Especially extension of reach collides with reducing the separation limits.
• Also increase of probing duration collides with motion speed.
• Generally the requirement for unambiguous locating requires a set of measured distances.

Such contracdictions result in challenges for systems performance and in hard restrictions concerning timely parallel availability of certain quality levels. Facing limitations as inevitable, the implementer of a locating systems has to determine the operational requirements first and then has to make a choice under a set of alternatives and must scale the adjoint limitations. The outcome is always a compromise with trade offs usually in budgetary effort and in technical precision. Any chosen alternative generally will exclude certain other technical options from operational availability.

Noisy ambience as a general condition

In technical terms, operational environments are generally noisy. For measuring that is not a friendly ambience. Systematic and stochastic errors under operational requirements and conditions turn virtually precise measures to fuzzy metrics. The measuring results get in worse in a densely populated ambience especially in the vicinity of other electrically active objects. Even physically passive surfaces contribute to the measurement problem. All physical effects tend to contribute unsteady and non linear behavior. Hence the physical measurement errors lead to biased or erratic results under such noisy conditions.

Frequency spread as an option

One escape from collision problems with wireless networks is the separation of the measuring and the communications processes with allocation to different frequencies, however requiring respective dual transponder capabilities. Another escape from collision problems with wireless networks is the spread of signals with stochastic coding.

Time as a restriction for measuring

Even if targets do not move, time is a restriction with the performing of a locating function. The first impact is that of allowed minimal distinct time differences that define the theoretically best resolution. This varies conceptually between phase discrimination in fractions of a cycle to be measured and full cycles to be counted. In competition for non-colliding transmission, time may appear as the main aspect with systems that use the very same frequency band. Other stochastic frequency allocation may ease the thrive for results, but normally coincide with lower allowance for power according to the set conditions of unlicensed usage.
Allowable time differences mostly vary with motion of the observed target. As for locating with absolute coordinates in a noisy environment several measurements are required and for disambiguation in space generally four measurements from independent reference points determine a target location, time appears as the sparse parameter.

Sequencing as a restriction

In general, the strict sequencing of tasks appears with single tasking in one processor. Similarly the factual sequencing on only one frequency results from anti collision procedures. Both types of sequencing produce some dilation of time (with anti collision) or some dilution of location (with moving targets), while the respective wireless processes are performed by each target.

Bandwidth as a restriction

The measuring of signals with steady modulation is bound to bandwidth of the modulated carrier. The measuring of chirped signals is equivalently bound to bandwidth of the transmitted pulses. In both methods the available bandwidth limits the precision of measurement.

Resolution as a restriction

Technical means for measuring offer limited resolution and respective digitizing errors. This limits again the quality of results. Any way to overcome such limits raises system cost. Hence the escape again is not in improving the technical effort, but directs to the mathematical yield.

Battery life cycle as a limiting factor

The use of primary or secondary cells in wireless nodes limits both the time of operation as well as the life cycle without change for fresh batteries or just recharging. The mode of operation will be designed accordingly to widen the span of battery supply. That may be achieved by sleep up mode with respective wake up circuitry, operating without receiver in connectionless beacon mode, low repetition cycles and optimally low transmission power. An integrated loading circuit raises cost but saves the cost for external contacts. An unchangeable primary battery improves by lower self discharge compared to secondary cells, but causes the need for complete replacement or at least of the casing facultatively.

Motion as a dynamic challenge

When a target moves at a certain speed, the sequential measuring of distances from such transmitter target to a set of responder targets may deliver distance data for the subsequent locations at each measuring directly back to the transmitter target. This effect is independent from architecture of the network.
However, a measuring triggered from the transmitter target but performed almost in parallel by a set of receiver targets delivers a much better result under motion conditions, but requires either a server function for collecting the resulting data or requires additional response back to the triggering transceiver target.
The other escape is to apply a procedure to bundle the required measurements for each target in direct sequence thus reducing one effect of motion challenge by saving the preparation times for a reporting communications link. If not, then the competition for non-colliding transmission will lengthen the time span for each set of transmissions.

Population as restriction

When several targets move independently in the same area or space and same wireless reach and also request locating independently and potentially in timely conflict using on the very same frequency for communications and for measurement, then the required measurements in one single ambience may collide. One escape again is the separation of the measuring and the communications processes with allocation to different frequencies, however requiring respective dual transponder capabilities.

Line of sight as a problem

In any case, line of sight is required for correct distance measurements. This may be eased by using auxiliary targets, but then increases the count of measurements. And the usage of auxiliary targets burdens the results with an increase of numeric inaccuracy.

Multipath propagation as a problem

Multipath propagation is inevitable with wireless systems. The reception from any transmitter and the response to any transmission are both challenged by the option of multiple propagation paths. If there is none but a single cranked path, there is no desired result at all, and the option to discriminate false measures from proper measures fails completely.
Typical issues with multipath propagation are fading, dither, diffraction, combining as non-linearity effects for the distance model. Additionally with power level measure the transmission through walls delivers rough errors, even with travel time measurement such error occurs.

Mathematical requirements and options

Mathematics serves for everything that cannot be covered by physics approaches. The assumption that a most qualified electro technical approach solves all problems arising from measurement is naïve and does not lead to sufficient results. At least thriving for best performance only at the expense of electronics is not an economized approach.
An operationally sufficient locating system will balance benefit and effort. Measurement and estimate shall take motion into account. This must not include the measuring of motion itself, but proper assessment of current and past motion to estimates. All estimate approximating the real location of the target is determined on the basis of a statistical model for the observed stochastic processes. Such model and estimation will use the set of observed propagation parameters. Some calibration data may serve as a basis for a statistical model of the propagation parameters. Such calibration is performed versus a spatial distribution of radio energy and with aspect to a known spatial distribution of corresponding targets. Other passive objects affecting propagation interfere with wireless operation and measurement.

Filtering as a basic requirement

Any measurement is always biased with disturbances from ambient radiation out of electrical units with switches, from other wireless units and from stationary equipment as computers. To eliminate erratic results, some estimation based on past behavior, current dynamic properties and with reference to coupling mechanisms is recommended. State of the art for such tracking is e.g. extended Kalman filtering. Approaches that do not apply filtering produce no reasonable results. However, scalar filtering uses the model of residence in a fixed location or stationary motion. If abrupt turning the direction of motion, the filter algorithm may totally fail until filtering has recovered from tracking a sufficient walk in the new direction has been performed.

Statistics as a means for estimation

In case of biased signals the prerequisite for filtering is some statistic estimation, which serves for eliminating the large errors and smoothes a sequence of measurement results. This may be integrated with filtering, as far as the eliminating of large errors does not bias the filtering process under any conditions.

Quadratic equations as a problem

The determining equations are quadratic ones, thus requiring at least one more equation (n+1) than defined by dimension (n). This leads to a minimum requirement of three equations for planar problems and four equations for spatial problems.

Over determination as a support

The common approach to locating calculations may be the inversion of the Euclidic distance equations. However, such deterministic approach does not serve for the balancing in over determined equation systems. The easy approach is the exploitation of Gauss’ least squares principle with the multi dimensional scaling according to Torgerson.

Wireless coexistence

Many offered systems architectures and product offerings use license free ISM frequency bands and reside in similar channel patterns. The operating of fuzzy locating shall not compromise the communications options. Some restrictions apply not to infringe this requirement.

Technology approaches and options

The second step after scalar calculation is the involvement of model data according to the dimensionality of the motion. If reference is made to targets in other planes but the plane on which the moving targets may operate, such model must be a three dimensional model. For model based operations, there are several options.

Coincident locating as the initial option

Imagine a worker operating with a handheld reader of any type. The person is skilled to capture the identity of an object and used reader will report the capturing with time stamp. Such report discloses the location of capture as far as this information is reported in contents. The mandatory condition could be some automatic means to capture the location at the moment of identifying. In all other cases the quality and reliability of the location report limits the validity of the e.g. vocally reported data.
In all implementations of automatic data acquisition and locating systems the option of locating a handheld reader in the moment of manual triggering shall be foreseen as the fall back option. Otherwise the robustness of automatic data acquisition systems operation is bound to availability of automatic operation only.

Choke point locating as the poorest option

A choke point is a static bottleneck in process flow designs. There the passage of individuals and/or objects may indicate the identity of such entity to a steadily installed identifier unit. This approach under all conditions is restricted to just one location.
Politics and Sales force may describe that as locating, but it is definitively still just identifying.

Power mapping as a first poor option

Propagation of radio signals happens according to Maxwell’s equations and includes attenuation in atmosphere proportional to distance, Such concept is the basis for power mapping. The irregularities from local ambient conditions may be taken into account by power measurement in the operational area to correct the theoretically linear attenuation with distance. However, this approach does not work with an accuracy of better than 10% of the calculated distances in the range of propagation, thus leading to accuracies in the range of some meters.

Time distance equivalence for radiation

Propagation of radio signals happens according to Maxwell’s equations and includes travel time in atmosphere proportional to distance, Such concept is the basis for precise distance measurement. The irregularities from local ambient conditions are not dominant, thus the approach is more precise than power measurement. So this approach works with an accuracy of better than 1% of the calculated distances in the range of propagation, thus leading to accuracies in the range of some centimeters. However, this approach serves as well for line of sight propagation as for indirect reflected propagation.

Space model as a strong option

To escape the biasing with secondary paths, there must be some reasoning that excludes the physically impossible locations from sets of results from locating. Simply, all calculated locations in material will be assessed as erratic, all calculated locations at distances not possible with inherent speed limits will be assessed as erratic and all locations above ground will be assessed impossible for floor operation. The requirement for space modeling leads to depicting the operational planes different from the limits to such planes, as walls, racks, and other installations.

Statistical model to exploit the measurements

There is no chance to base stable results for location on single measurements. Statistics allow for

• combining subsequent measurement results to form a track
• smoothing a single location from subsequent measurement results
• iterating stable results from coarse first estimates

The methods for computing a set of results are described in context of various applications not just with locating technologies.

Fuzzy reasoning with discrete spatial compartments

As far as locating just has to support discrimination of rooms where a target may reside, the continuous model approaches may be combined with reasoning procedures to eliminate improbable results and to exclude operationally invalid locations from potential depicting a scenery. The known methods of inference apply to such processing.

Geometric mapping contributions to reasoning

As far as the ambient operational conditions are stable, a geometric mapping of the neighborhood may support the reasoning. Then all massive obstacles describe the residual space of operation. As well such mapping will support the systematic and well determined consideration of multipath propagation effects. Hence geometric mapping derives the major gain compared to Bayes' estimators.

Adaptive approaches

A common approach as preparatory mapping requires steady conditions and a constant ambience. This crucial condition is not fulfilled in dynamic operational theatres. However, a robust solution will always detect and investigate the actual conditions and reconnoiter the present ambience. For robot navigation, the methods of adaptive systems design, hence application of learning functions, is state of the art. However, adaptation requires time. A fully adaptive solution not applying a priori knowledge will be rather slow and will show limited dynamics. A balanced combination of adaptive functions will allow for best performance in a generally known ambience and cope for all changes that occurred after last encounter.

Operational requirements

Locating arises from operational challenges. Traditional understanding of well kept enterprises with well educated staff is undermined with a thriving for reduced skills to achieve lesser cost. In result and in addition with continuing socio-economical disparities the processes and objects under control are threatened by negligence, fraud and theft.

Evidence

A simple indication of presence is given with the signal used for locating an object or a person. However, as presence may be temporary, a time stamp is required to adduce evidence in retrospective.

Cooperation requirement

Persons carrying transponders or tagged objects with transponders might not be willing to be observed though having agreed earlier to this process. Then cooperation may be technically required, but individually denied. The robustness of the detection hence shall not be dependent to such cooperation. Especially covering the transponder or tearing off the transponder or otherwise tampering must be sensed automatically.

Proof of presence

The presence of an object or a person in an operational vicinity is a strong demand. Absence of required resources generally affects planned processes. Therefore the proof of presence may be performed as far as possible before binding of additional resources happens.

Co-locating of staff

Specially team work is bound to availability of required staff. The persons involved in a scheduled operation are well skilled to determine who is missing, but locating the missing parties is not that easy and may be strongly improved by system support.

Discrimination of rooms

To allow for operation the respective room shall coincide with the scheduled action. Any request to operate under restrictions outside the planned confined area is suspect and may challenge security of processes and of secured knowledge. Locating the acting entities in the named confinement contributes to fulfilling security requirements.

Coincidence of presence and challenge

A person may try to access secured data, material or other resources outside the well secured rooms or areas. However, control may not always secure the subordination of the user to given orders. Locating simply in close distance or just in contiguity to allowed work positions may confirm the request for access as a basic feature.
Other application is coincidence of service provider, e.g.physician, with service requestor, e.g. patient, in a hospital. After identifying both persons as estimating their radial distance then access to the patient's file may be granted without any error. Such function would not be viable with precise or crisp systems as precision and allowable cost are in contradiction with absolute coordinate estimates.

Quality requirements

The above listed terms will show that the definition of desired precision and accuracy, of repeatability and delays alone does not comply with a proper definition of requirements under aspects of cost. However, other terms of quality apply without restrictions.

Tamper proof identity

Basic requirement for any means to support locating is a tamper proof inherent identity of the carrying target with secured access. The secrecy of the identity prevents from plump copying threat and the tamper protection prevents from manipulating the target.

Self identifying authenticity

Persons who pursue to access data and applications normally authenticate themselves. Such authentication is generally bound to known locations, where the persons are authorized to perform work. Locating persons when they challenge authorization procedures is and advantage to prevent from fraud and theft.

Object identifying security

Numerous means are known to identify objects. Normally the location where hand held units are operated are just roughly determined by the access point where connection to network is made. However such locating is still an improvement in many operations to secure knowledge about whereabouts of objects upon identifying.

Tracking capability

In larger context of spatially distributed services and especially in logistics, numerous objects are in use in parallel, in different locations or on the move. Especially with transportation whereabouts of objects are understood as an essential to achieve high quality of service. As far as trust is with the forwarder, no problem exists on the journey and locating may happen just on leave and upon arrival. But third party infringements may collide with this assumption and generate a demand for permanent tracking on the journey as well. Then fuzzy locating is an economized and sufficient approach, which shall not provide location data with high metric accuracies, but status information with checkable and justifiable evidence.

Tracing capability

In case single objects are lost, the capability to trace the whereabouts is another option to get access to the missing target again. However, this tracing is performed on yet available data and no means will deliver the data from the past without respective precautions. Especially in transportation whereabouts of lost objects are understood as an essential to retrieve the missing belongings.

Alert on deviation

Easily any deviation from planned course, set route and scheduled arrival may lead to an alert. This requires timely locating and comparison of captured data with planning.

GPS Global Positiong System Modernization

GPS modernization

The United States' Global Positioning System (GPS), having reached Fully Operational Capability on July 17, 1995^[1] has completed its original design goals. However, additional advances in technology and new demands on the existing system led to the effort to modernize the GPS system. Announcements from the Vice President and the White House in 1998 initiated these changes. In 2000, U.S. Congress authorized the effort, referred to as GPS III.
The project involves new ground stations and new satellites, with additional navigation signals for both civilian and military users, and aims to improve the accuracy and availability for all users.
Lockheed Martin was awarded the GPS III Space Segment contract on May 15, 2008. The first launch is projected for 2014.^[2] Raytheon was awarded the Next Generation GPS Control Segment (OCX) contract on Feb 25, 2010.^[3]

New Navigation Signals

Civilian L2 (L2C)

One of the first announcements was the addition of a new civilian-use signal to be transmitted on a frequency other than the L1 frequency used for the existing GPS Coarse Acquisition (C/A) signal. Ultimately, this became known as the L2C signal because it is broadcast on the L2 frequency (1227.6 MHz). It is transmitted by all block IIR-M and later design satellites.
The L2C signal is tasked with providing improved accuracy of navigation, providing an easy-to-track signal, and acting as a redundant signal in case of localized interference.
The immediate effect of having two civilian frequencies being transmitted from one satellite is the ability to directly measure, and therefore remove, the ionospheric delay error for that satellite. Without such a measurement, a GPS receiver must use a generic model or receive ionospheric corrections from another source (such as a Satellite Based Augmentation System). Advances in technology for both the GPS satellites and the GPS receivers have made ionospheric delay the largest source of error in the C/A signal. A receiver capable of performing this measurement is referred to as a dual frequency receiver. The technical characteristics of it are:

• L2C contains two distinct PRN sequences:
  • CM (for Civilian Moderate length code) is 10,230 bits in length, repeating every 20 milliseconds.
  • CL (for Civilian Long length code) is 767,250 bits, repeating every 1500 milliseconds (i.e., every 1.5 s).
  • Each signal is transmitted at 511,500 bits per second (bit/s), however they are multiplexed to form a 1,023,000 bit/s signal.
• CM is modulated with a 25 bit/s navigation message with forward error correction, whereas CL is a non-data sequence (it does not contain additional modulated data).
• The long, non-data CL sequence provides for approximately 24 dB greater correlation protection (~250 times stronger) than L1 C/A.
• L2C signal characteristics provide 2.7 dB greater data recovery and 0.7 dB greater carrier tracking than L1 C/A
• The L2C signals' transmission power is 2.3 dB weaker than the L1 C/A signal.
• In a single frequency application, L2C has 65% more ionospheric error than L1.

It is defined in IS-GPS-200.^[4]

Military (M-code)

A major component of the modernization process, a new military signal called M-code was designed to further improve the anti-jamming and secure access of the military GPS signals. The M-code is transmitted in the same L1 and L2 frequencies already in use by the previous military code, the P(Y) code. The new signal is shaped to place most of its energy at the edges (away from the existing P(Y) and C/A carriers).
Unlike the P(Y) code, the M-code is designed to be autonomous, meaning that users can calculate their positions using only the M-code signal. P(Y) code receivers must typically first lock onto the C/A code and then transfer to lock onto the P(y)-code.
In a major departure from previous GPS designs, the M-code is intended to be broadcast from a high-gain directional antenna, in addition to a wide angle (full Earth) antenna. The directional antenna's signal, termed a spot beam, is intended to be aimed at a specific region (i.e. several hundred kilometers in diameter) and increase the local signal strength by 20 dB (10X voltage field strength, 100X power). A side effect of having two antennas is that the GPS satellite will appear to be two GPS satellites occupying the same position to those inside the spot beam.
While the full-Earth M-code signal is available on the Block IIR-M satellites, the spot beam antennas will not be available until the Block III satellites are deployed, tentatively in 2013.
Other M-code characteristics are:

• Satellites will transmit two distinct signals from two antennas: one for whole Earth coverage, one in a spot beam.
• Modulation is binary offset carrier
• Occupies 24 MHz of bandwidth
• It uses a new MNAV navigational message, which is packetized instead of framed, allowing for flexible data payloads
• There are four effective data channels; different data can be sent on each frequency and on each antenna.
• It can include FEC and error detection
• The spot beam is ~20 dB more powerful than the whole Earth coverage beam
• M-code signal at Earth's surface: –158 dBW for whole Earth antenna, –138 dBW for spot beam antennas.

Safety of Life (L5)

Safety of Life is a civilian-use signal, broadcast on the L5 frequency (1176.45 MHz). In 2009, a WAAS satellite sent the initial L5 signal test transmissions. SVN-62, the first GPS block IIF satellite, continuously broadcast the L5 signal starting on June 28, 2010.

• Improves signal structure for enhanced performance
• Higher transmission power than L1 or L2C signal (~3dB, or twice as powerful)
• Wider bandwidth, yielding a 10-times processing gain
• Longer spreading codes (10 times longer than used on the C/A code)
• Located in the Aeronautical Radionavigation Services band, a frequency band that is available world wide.

WRC-2000 added space signal component to this aeronautical band so aviation community can manage interference to L5 more effectively than L2
It is defined in IS-GPS-705.^[5]

New Civilian L1 (L1C)

L1C is a civilian-use signal, to be broadcast on the same L1 frequency (1575.42 MHz) that currently contains the C/A signal used by all current GPS users. The L1C will be available with first Block III launch, currently scheduled for 2013.

• Implementation will provide C/A code to ensure backward compatibility
• Assured of 1.5 dB increase in minimum C/A code power to mitigate any noise floor increase
• Non-data signal component contains a pilot carrier to improve tracking
• Enables greater civil interoperability with Galileo L1

It is defined in IS-GPS-800.^[6]

Block III satellite improvements

Increased signal power at the Earth's surface

• M-code: –158 dBW / –138 dBW.
• L1 and L2: –157 dBW for the C/A code signal and –160 dBW for the P(Y) code signal.
• L5 will be –154 dBW.

Researchers from The Aerospace Corporation confirmed that the most efficient means to generate the high-power M-code signal would entail a departure from full-Earth coverage, characteristic of all the user downlink signals up until that point. Instead, a high-gain antenna would be used to produce a directional spot beam several hundred kilometers in diameter. Originally, this proposal was considered as a retrofit to the planned Block IIF satellites. Upon closer inspection, program managers realized that the addition of a large deployable antenna, combined with the changes that would be needed in the operational control segment, presented too great a challenge for the existing system design^[7]

• NASA has requested that Block III satellites carry laser retro-reflectors.^[8] This allows tracking the orbits of the satellites independent of the radio signals, which allows satellite clock errors to be disentangled from ephemeris errors. This is a standard feature of GLONASS, will be included in the Galileo positioning system, and was included as an experiment on two older GPS satellites (satellites 35 and 36).^[9]

• The USAF is working with NASA to add a DASS payload to the second increment of GPS III satellites as part of the MEOSAR system.^[10]