Main Industrial and Commercial Applications As opposed to most of the military applications which demanding high performance under extreme environment, commercial and industrial applications are even more demanding concerning quality/cost ratio. Rubidium-Atomic-Standard Technology meets the needs of numerous commercial and industrial applications. As mentioned above Rubidium standards represent a middle solution between quartz and atomic oscillators of high quality (Cs and maser H) when considering the quality/cost ratio.   Digital broadcasting (DAB-DVB) Television and audio broadcasting are undergoing a continuous process of integration and digitalization. Signal complexity increases due to the more complex information that willl be transported by the relevant technologies (e.g. DVB, DAB) as well a tighter connection between internet and television / audio broadcasting. The underlying digital technologies impose new stringent requirements regarding towards synchronization. Tighter synchronization performances are indeed needed to achieve the requested Quality of Service. One way of doing that is by the widespread of rubidium frequency standard. The main forms of digital radio and television are Digital Audio Broadcasting (DAB), Digital Video Broadcasting (DVB), DVB-S (Digital Video Broadcasting–Satellite) and Digital Video Broadcasting - Terrestrial (DVBT). These new broadcasting forms make all use all synchronous transmission technologies at various levels both for the carriers and for the signals. DAB - Digital Audio Broadcasting is a digital transmission system for radio broadcasting, using dedicated receivers. In addition to audio data (voice and music) DAB allows to the transmitting of video and information data at low data transfer rates as well as value-added services such as a news-ticker. DVB – Digital Video Broadcasting group was created in order to establish a technical framework for the introduction of digital broadcasting systems to suit the whole range of delivery mechanisms, including cable, satellite, terrestrial and MMDS (multimedia digital services). DVB has already developed a coherent set of methods to bring digital television to home. The DVB standard itself is a generic term for various technical specifications and various transmission methods such as DVBT (terrestrial – COFDM technology), DVB-S (satellite – QPSK), and DVB-M (cable – QAM). In the initial phase DVB focuses on stationary applications such as home television. In a later second phase the extensive usage in mobile applications is planned. Furthermore, the integration of manufacturers, regulators, network operators, and broadcasters create a wide basis of acceptance.   Space Applications: GPS, Galileo, Glonnass, SATCOM Atomic Clocks are used in various space applications: examples are GNSS and SATCOM Satellites GNSS (navigation) systems such as GPS, Galileo and Glonass uses atomic clocks as the key component to provide the accurate timing needed for the navigation process. A communication satellite (sometimes referred to in short as ComSat) is a satellite stationed in space for the purposes of telecommunications. Modern communications satellites use geostationary orbits, Molniya orbits or low polar Earth orbits. A satellite communication system is built up from two main sub systems: the satellite and the satellite base stations. Atomic clocks on board and in the base station are essential for precise timing.   Israel Aircraft Industries MBT/Space Division and AccuBeat Company Ltd. have signed an Agreement for Developing of new Space Atomic Rubidium Clock AccuBeat and IAI/MBT Space Division are chosen by Europe to supply Atomic rubidium clocks for the Galileo Ground Station   Test Equipment, Calibration and Scientific Labs Introduction Atomic frequency standards, kept in metrological laboratories, are being used as “primary” frequency and time standards for the calibration of secondary time/frequency standards. Secondary time standards may be used for local calibration of laboratory instruments, seismic data collection, or as a basic ingredient of the calibration services. These users may be interested only in standard frequency dissemination, thus releasing stringent accuracy requirement on the primary source, but usually they ask for traceability to international standard. Such traceability should be recognized by international accreditation bodies. Under following heading you will find more information about the few of the test equipment, calibration and scientific labs' applications: Calibration Laboratories In the last decade most countries have established dedicated networks of calibration laboratories in order to transfer the traceability from national standards to instruments used at production level. The accredited calibration laboratories must ensure the traceability of their metrological standards to the national primary standards. In case of time and frequency quantities, the calibration laboratories have their own frequency standard – cesiums or disciplined rubidium, and the Traceability is ensured by means of different techniques that range from Radio coded signals, Telephone time codes, LF broadcasts, television broadcasts and navigation satellite broadcasts. Frequency sources used as reference in calibration laboratories usually are rubidium frequency standards, GPS disciplined. Calibration labs need a frequency reference and not a “time tagging reference”, i.e. they must calibrate frequency or time interval standard, not dating devices. The relative uncertainty on the knowledge of the frequency is at the level of 10-13 at best. Considering the transmission path and the uncertainty sources depicted in the Figure 8.2-1, some requests may relaxed. Indeed in frequency comparison systems all the “fixed” or stable delays may disregarded. Over the past years, most of the calibration laboratories bought their own frequency standards, usually an atomic one based on the rubidium or cesium atom. To ensure traceability, then they had to buy also a comparison system as well. Therefore the devices and the amount of money were twofold. Now, with the availability on the market of rubidium frequency standards disciplined to GPS, the market of stand alone frequency standards has dramatically decreased. Space Exploration How does NASA know where a spacecraft is in deep space? The spacecraft's precise range, velocity and angular position are determined by the aid of highly stable frequency standards. The range is determined using information from the propagation time of microwave radiation between an antenna on Earth and the spacecraft. The velocity is determined from the "doppler," i.e., by comparing the phase of the incoming carrier signal with that of a reference signal generated from the ground station frequency standard. The angular position is determined by very long baseline interferometry (VLBI) in which widely separated stations (in California, Spain and Australia) simultaneously receive signals from the spacecraft. Differences between times of arrival coupled with knowledge of the baseline vectors joining the station antennas provide direct geometric determination of the angles between the baseline vectors and the direction to the spacecraft. Hydrogen masers (see chapter 6) provide the best stability (~10-15) for the propagation times of interest, which typically range from minutes to hours. VLBI is also used for high resolution angular measurements in radio astronomy. High Resolution Counter A frequency counter is an electronic instrument, or component of one, that is used for measuring frequency. Since frequency is defined as the number of events of a particular sort occurring in a set period of time, it is generally a straightforward to measure it. Most frequency counters work by using a counter which accumulates the number of events occurring within a specific period of time. After a preset period (1 second, for example), the value in the counter is transferred to a display and the counter is reset to zero. If the event being measured repeats itself with sufficient stability of frequency and this frequency is considerably lower than that of the clock oscillator being used, the resolution of the measurement can be greatly improved by measuring the time required for an entire number of cycles, rather than counting the number of entire cycles observed for a pre-set duration (often referred to as the reciprocal technique). The internal oscillator which enables the frequency counter to measure time is called the timebase, and must be calibrated very accurately. If what is to be counted is already in electronic form, simple interfacing to the instrument is all that is required. More complex signals may need some conditioning to make them suitable for counting. Most general purpose frequency counters will include some form of amplifier, filtering and shaping circuitry at the input. Other types of periodic events that are not inherently electronic in nature will need to be converted using some form of transducer. For example, a mechanical event could be arranged to interrupt a light beam, and the counter made to count the resulting pulses. Frequency counters designed for radio frequencies (RF) are also common and operate on the same principles as lower frequency counters. Often they have more range before they overflow. For very high frequencies, many designs use a high-speed prescaler to bring the signal frequency down to a point where normal digital circuitry can operate. The displays on such instruments take this into account so they still read true. If the measured frequency is too high for any prescaler, a mixer and a local oscillator can produce a suitable frequency to measure. The accuracy of a frequency counter is greatly dependent on the stability of its timebase. Highly accurate circuits are used to generate this for instrumentation purposes, usually using a quartz crystal oscillator within a sealed temperature-controlled chamber known as a crystal oven or OCXO (oven controlled crystal oscillator). For higher accuracy measurements, an external frequency reference tied to a very high stability oscillator such as a GPS disciplined rubidium oscillator may be used. Where the frequency does not need to be known to such a high degree of accuracy, simpler oscillators can be used. It is also possible to measure frequency using the same techniques in software in an embedded system. A CPU for example, can be arranged to measure its own frequency of operation provided it has some reference timebase to compare with. High Performance Synthesizers A frequency synthesizer is an electronic system for generating any of a range of frequencies from a single fixed timebase or oscillator. They are found in many modern devices, including radio receivers, mobile telephones, radiotelephones, walkie-talkies, CB radios, satellite receivers, GPS systems, etc. Coherent techniques generate frequencies derived from a single, stable master oscillator. In most applications, crystal oscillator are common, but Rubidium frequency sources can be used in high performance requirements. Special Test Equipment With greater expansion of wireless cells the need for rubidium standards for field service and calibration is growing. For example, new handset designs must meet the standards expected by the consumer and that means carrying out earlier and more comprehensive development, design verification and regression testing. In some of the solutions rubidium frequencies standards are required as frequency references.   Software Defined Radio Technology A software-defined radio (SDR) system is a radio communication system which can tune to any frequency band and receive any modulation across a large frequency spectrum by means of programmable hardware which is controlled by software. An SDR performs significant amounts of signal processing in a general purpose computer, or a reconfigurable piece of digital electronics. The goal of this design is to produce a radio that can receive and transmit a new form of radio protocol only  by running new software. The scheme of any digital receiver consists of an antenna circuit, followed by low-noise amplifiers and one or more intermediate frequency conversion phases (IF-phases). Nowadays, the predominant trend is to convert the information signal into a numerical form and to elaborate samples by means of numerical techniques in order to execute all the main phases of a digital receiver. This tendency brings to a technology named Software Radio. The hardware of a software-defined radio typically consists of a super-heterodyne RF front end which converts RF signals from (and to) analog IF signals, and analog to digital converter and digital to analog converters which are used to convert a digitized IF signal from and to analog form, respectively. Software radios may be particularly utilized for the military and cell phone services, both of which must serve a wide variety of changing radio protocols in real time. Software-defined radio can currently be used to implement simple radio modem technologies. In the long run, software-defined radio is expected by its proponents to become the dominant technology in radio communications. It enables the enabler of the cognitive radio. Many Software Radio (SR) designs have been proposed. The main differences are in architecture and in the boundary point where transition from analog to digital Signal Processing (SP) occurs. From a SP point of view, it is best to push the digital processing as close to the antenna as possible. With device densities and clock speeds increasing constantly, the development of an operating system environment suitable for programming a host of protocols and operating over a wider and wider RF bandwidth can be expected. A likely scenario is that a reconfigurable hardware will become a common part of the “microprocessor”. This transition will allow morphing of the computational environment based on the application for speed optimization. The performance of the free oscillator (piloting the ADC) is expected to be a crucial point for the correctness of the SDR operations. Theoretical comparison between the performance of SDR with quartz and rubidium clocks in a carrier recovery system show that optimum performance will be achieved by using rubidium oscillators were employed both in transmission and reception, as they present values of instability of the order of 1E-13.   Time Tagging for General Users Introduction These general applications are mentioned here only for additional information, since in a very few cases rubidium standards are used or proposed. Applications needing high accurate or reliable time references: E-commerce, Time stamping authorities, Computer networks synchronization Timekeeping protocol devices Measurement laboratories inside manufacturers producing electronic equipment Factories and industrial laboratories needing time and frequency references for their daily activities Applications needing less accurate or reliable time references: Banks and financial companies Clock synchronization for working time control Environmental parameters controls, Traffic lights regulations Clock manufactures and sellers Stamping of expiration data on alimentary goods Airport and main station clocks POS systems Sport performance measuring devices A Quick descriptions of Main Applications E-Commerce One of the major concerns in todays e-commerce is the security of information provided by the customer within a purchasing process. Access by hackers or other intruders to information such as credit card numbers must be ensured. This requirement calls for a trusted system of encryption. A trusted time signal should be implemented into a comprehensive and reliable encryption system. As regards the E-commerce, an estimate for the USA market valid for mid 1999, is a billion of dollars and is reported here: E-Banking Electronic banking is subject to various risks: unauthorized access to documents, accounts, credit cards, falsified transactions, etc. Time / data stamping upon the basis of legally traceable time could contribute to a modular security system in order to reduce or even exclude these risks. Online Stock Exchange Activities In addition stock exchange activities are subject to various risks that are partly identical with those in ebanking. Shifting more and more activities from conventional trade to online-trading systems has raised another issue of significant importance: the need for an accurate and legally accepted documentation providing the following information: who has ordered what when and for which amount? Here is again the importance of an internationally legally - accepted timing signal visible. Quality Assurance Systems Quality assurance has become important since product liability increases the responsibility to their costumers of the producers for all kinds of goods (food/non-food) towards their customers. In all developed industrialized countries there already exist laws that impose stricter product liability. In order to meet legal documentation requirements for the entire production process, the implementation of a system is recommended that ensures the usage of internationally acknowledged and traceable time. NTP / Encrypted NTP (Network time protocol) The security features of NTP / encrypted NTP could be enhanced by the implementation of accurate time signals. Secure Electronic Document Transfer By companies, institutes, hospitals, notaries Date and time stamping These applications are spreading rapidly all over the world, and in every country special dedicated services are being implemented. The needed reliability and traceability usually are provided by the national metrological centers. Computer network synchronization As regards the computer networks synchronization market, the customers’ needs are satisfied in addition to the the already mentioned ones by the Internet network time protocol services, These are in most case synchronized by GPS time signals. The number of users of some of these services differs enormously from the number of the receivers purchased because they are frequently distributed along a dedicated network. A typical example of such a configuration is the Internet time synchronization, provided by a limited number of primary (stratum 1) servers, which can be accessed by millions of users.   Transport Many application in transport industry has increasing requirement for accurate time & frequency sources. Air Traffic control  - aims to ensure safety and efficiency of flight operations, on the ground and in the air. Today, air transport faces major challenges. Affordability, efficiency, safety, environmental friendliness and technical modernization are central to air travel development. Air transport play main role in the overall globalization ensuring the rapid and efficient movement of people and goods, but also providing essential access to remote regions. In Europe the EU start running a program called SESAR aims to provide the answer, by developing a new generation of Air Traffic Management systems, which can in turn serve as a model for the world.   Cellular networks (CDMA and UMTS) Synchronization of data streams is required in Wireless third-generation technologies like UMTS and cdma2000 to ensure reliable signal handoff between basestations. With the increasing demand for high-bandwidth and real-time application, dropped connection are becoming intolerable. The solution is to establish effective management and distribution of a reliable reference clock throughout the entire network. Theoretically it was tempting to use the public-switched telephone network (PSTN) as the source for synchronization and distribute it via T1/E1 links to the rest of the network. Unfortunately, using the PSTN is not impracticable for many reasons: first the quality of the PSTN cannot be certain, excessive jitter and wander are add during transit. Practically, wireless networks generally operate using a reference clock backed by a holdover clock. All other network clocks must be traceable to the reference clock. The question is how to distributing a reliable reference clock throughout the entire network. GPS system can offer independent reference for any application, including wireless Time synchronization is not easy. It take time to propagate a reference clock to the users. Each line and nodes add error. After you set the user clock it will start to drift, so continuous recalibration is needed. Even when using one reference clock for entire network you can have a situation when subsystem start to deviate at different rate until the connecting will start to drop. CDMAone and cdma2000 demand that the deviation will not exceed 1 part in 1,010 or 7.5 microseconds over a 24-hour period. Comparatively, UMTS wideband code-division multiple access (W-CDMA) and GSM networks require an accuracy of 5 parts in 108 or 4.3 milliseconds. To reach this level of synchronization subsystem must track a reliable reference clock and also have excellent holdover abilities in case the reference clock is not available. The reference clocks used to be sent over the network itself. It is an appropriate way most of the time, but it cannot guarantee adherence to the minimum requirements for high-speed data transfers across highly constrained wireless networks under all operating conditions. GPS is an excellent candidate for transporting a reference clock because each subsystem can have a direct connection to the same reference clock instead of an indirect connection over an unreliable network link. GPS is not all the time available. You might have a situation when not enough satellites or environmental conditions make the signal difficult to lock onto. In this case you need to have an holdover capability. Holdover starts when a clock holds the last frequency at which it was clocking when the reference clock signal failed to arrive. Two standard types of clocks used in basestations today that are up to the task of accurately holding a reference clock with such accuracy are highly precise ovenized quartz oscillators and rubidium atomic clocks. Quartz oscillators are the less-expensive option but require additional components. For example, quartz performance changes over temperature, so this has to be managed. Rubidium atomic clocks, on the other hand, provide reliability that's an order of magnitude greater than CDMA networks require. The primary difference between the two clocks is reflected during loss-of-power scenarios and how long it takes the clock to regain stability once the reference source has been lost. Quartz clocks can take four to 24 hours to stabilize frequency. As the quartz warms, its stability increases. Rubidium atomic clocks achieve 98 percent reliability within minutes. Rubidium units achieving lock within a 5-minute window with an absolute accuracy better than 1 part per billion. In contrast, quartz resonators depend on the bulk acoustic properties of a crystal and can take hours to achieve wireless levels of accuracy, even with a GPS reference. As in UMTS technology there is no need for an absolute time code you can used a local clock as a reference source as long as its long term stability is 50 parts per billion over a 10-year period. This level of stability is in the very high level of quartz technology and easily achievable by Rubidium atomic clock. Rubidium can run for longer than 10 years and exceed the UMTS requirements. Positioning systems in cellular networks There are a number of reasons for which it is useful to be able to pinpoint the position of a mobile telephone: location sensitive billing, increased subscriber safety, intelligent transport systems (ITS), enhanced network performance and so on. The principal positioning techniques are: Propagation Time (PT), this involves measuring the time it takes for a signal to travel between a base station and a mobile station or vice versa. Time difference of arrival (TDOA), a mobile station can “listen” to a series of base stations and measure the time difference between each pair of arrivals. If the base stations are transmitters, the transmitted signal must leave each base station at the same time or with a known offset; if the base stations are receivers there must be a known time relationship between the receiver clocks at these base stations. Angle of arrival (AOA), this involves measuring the angle of arrival of a signal from a base station at a mobile station; synchronization is not required. Carrier phase (CP), the phase of a carrier has the potential to provide position evaluations with an error less than the carrier wave length. The need is to maintain a continuous lock on the carrier signal. Failure to do so results in cycle slips and errors in position. In the GSM system a combining of the previous techniques is generally used; some studies have demonstrated that performances improve through the TDOA technique and in presence of BTS synchronism. In UMTS system best results are obtained through Time Aligned Idle Period Downlink (TA-PDL) technique, in which the mobile is required to make Time of Arrival measurements during the idle period of the serving base site and these periods are approximately time aligned in adjacent BTS. The utilization of rubidium clocks will be indispensable to offer location and positioning services in future mobile networks. Testing technology for wireless devices and network As wireless technologies have evolved over multiple generations, handsets and network infrastructure have become more complex and test requirements increasingly challenging. Atomic Rubidium Standard are use in the Handset Testing and Network Measurement devices.   Wireline Network Communication Introduction Synchronization in telecommunication networks plays a very important role: the main reason is that it has a great influence on the system performances and the quality of services offered by the network operators to the users. Synchronization is of fundamental importance at both the application level (voice, audio, video and graphics) and at the transmission level (packet, cell, symbol and bit). If the synchronization is not accurate enough and the network can not store the informative units, a certain amount of data is lost and the throughput decreases. To avoid this problem, all the network entities need to be synchronized with a high accuracy. In order to maintain the bit flow integrity through a telecommunication network, an accurate synchronization signal to timing the bit reading is needed. In a wide area network the condition of a perfect synchronism is not achievable because of the phase fluctuations along the transmissive vectors and in the network nodes. High frequency phase variations are referred as jitter, while low frequency ones are referred as wander. A frequency of 10 Hz is generally used to delineate wander from jitter. To avoid synchronization problems, accurate clocks are used. There are two kinds of clocks: autonomous clocks and slaved clocks. The first ones produce a chrono-signal by themselves, while the second ones are slaved to an input signal and produce an output signal locked to the input one by means of a PLL. If the input signal fails they can generate an output in the holdover mode. The clocks used in hierarchical networks may be divided into three different groups according to their features and the performances required by the international normative: primary reference clocks, synchronization supply units and equipment clocks. Primary reference clocks are the most important entities in a synchronization network, because they produce the synchronization signal directly or indirectly used by all the other network clocks. This signal degrades from the higher levels to the lower ones: for this reason, it must provide an excellent long-term stability of 10-11/life. The most suitable clocks are cesium standards or hydrogen MASER. The Synchronization Supply Units (SSU) consist of an oscillator and a PLL to serve the output signal to an input reference. This kind of clock must be able to filter noise and phase discontinuities affecting the reference signal. Moreover, it has to maintain a stability level of 10-9/day, 10-8/day in holdover mode. The most suitable clocks are rubidium standards or some high performance quartz clocks. Equipment clocks are generally constituted by quartz oscillators slaved to the supply units: in fact, in presence of a good reference, high performances are not required (10-6/day). This kind of clocks is very cheap in respect to the other standards and provides a very good short-term stability. SONET/ SDH (Synchronous Digital Hierarchy) Synchronous optical networking, is a method for communicating digital information using lasers or light-emitting diodes (LEDs) over optical fiber. The method was developed to replace the Plesiochronous Digital Hierarchy (PDH) system for transporting large amounts of telephone and data traffic and to allow for interoperability between equipment from different vendors. Synchronous networking differs from PDH in that the exact rates that are used to transport the data are tightly synchronized across the entire network, made possible by atomic clocks. This synchronization system allows entire inter-country networks to operate synchronously, greatly reducing the amount of buffering required between elements in the network. The SDH network structure is based on the hierarchical strategy: the reference signal is distributed from the primary clock (PRC) to the lower layers. PRC is the first layer clock, while in the intermediate network nodes the SDH supply units (SSU) are used. SSU are generally interconnected by equipment clocks (SEC) chains of limited length to prevent from excessive signal degradations. As for Synchronization sources available to a SONET NE, these are: Local External Timing. This is generated by an atomic Cesium clock or a satellite-derived clock, like GPS-Disciplined Rubidium, by a device located in the same central office as the SONET NE.   Line-derived timing. A SONET NE can choose (or be configured) to derive its timing from the line-level, by monitoring the S1 sync status bytes to ensure quality.   Holdover. As a last resort, in the absence of higher quality timing, a SONET NE can go into "holdover" until higher quality external timing becomes available again. In this mode, a SONET NE uses its own timing circuits to time the SONET signal. ATM (Asynchronous Transfer Mode) The ATM networks transfer information through cells of 53 byte and the bit rates supported are 155.2 Mbit/s and 622.8 Mbit/s. ATM can transfer either constant or variable bit rate services, but because of the asynchronous nature of the system, there are any problems in the AAL layer to the receiver in reconstructing the symbol rate of the source. In fact, arrival cell rate is variable and during the transfer through the network some cells may be lost or affected by jitter and wander. For this reason, an opportune dimensioning of the traffic control parameters and a sort of low pass filtering of the cell interarrival time are needed. There are, at least, three sources of jitter associated to the cell transfer technology: Bursty nature of the traffic   Statistical multiplexing in the network nodes   Source jitter (a variable delay in filling up the payload of the cell) In ATM connections the transmitter plays the role of the master and the receiver the slave, bringing to a point-to-point architecture. There are three possible methods of synchronization of ATM traffic streams: Immediate playout: consist in releasing the data to the application as soon they enter the AAL receiver.   Adaptive playout: consist in buffering in the AAL receiver the input traffic, in order to smooth cell transmission jitter   Synchronous residual timestamp: (SRTS), consist in injecting appropriate Residual Timestamps in the transmitted data stream. A RTS encodes the difference between the service clock frequency and a common clock frequency. Rubidium clocks can be used inside the cross-connect nodes of the ATM network for distribution of synchronization in the network infrastructure for the long-term stability because of there good performances in holdover Periods. Network time Servers, NTP NTP is used, inside the Internet architecture, to synchronize hosts and routers; a lot of services are based on NTP, for example NFS, file transfer and E-commerce. NTP architecture is quite similar to the hierarchical architecture adopted in the digital telephone networks: each level is called stratum. At the first level of the hierarchy, we find time servers that are connected to a primary reference clock, such as accurate GPS receivers and atomic clocks. The utilization of atomic clocks in this architecture could be useful in timeservers combined to a GPS receiver. A unique primary signal for the synchronization could not be sufficient because GPS signal gives no continuity guarantees. Atomic clocks can also be used in the 2nd stratum of the hierarchy for the distribution of the network synchronization.

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