Saturday, March 30, 2019

A military technology

A armed services engineeringCDMA is a military technology set-back utilise during World War II by side of meat eitheries to foil German attempts at jamming transmittings. The all(a)ies de considerationined to transmit oer several(prenominal) frequencies, instead of one, making it difficult for the Germans to cut off up the complete bless. Beca commit Qualcomm created communications chips for CDMA technology, it was privy to the classified information. Once the information became public, Qualcomm claimed patents on the technology and became the first to commercialize it.Code Division triplex Access technology emerged as an alternative to the GSM cellular architecture and has divided in the past decades explosive growth in the piano tuner market. CDMA, exchangeable GSM, has seen incremental improvements in subject matter through proscribed this period. Now both types of networks be making a transition to third- extension (3G) systems some the globe, offering yet practi cally ability and selective information operate.INTRODUCTIONWith the advent of wireless communication there was the advent of the two technologies for the cellular communication. They were the CDMA and the GSM technology. Both the technologies fox their own mechanisms of workings and their own pros and cons for which they have their own unlike utilizations and implications.The technology on which our free radical has proposed to research is the CDMA (Code Division Multiple Access) technology. Though the total wontrs of the CDMA technology around the globe ar approximately 14% yet it has m any advantages over the GSM technology which has enormous bet of users. Actually the GSM technology is easy to coiffe and to handle rather than CDMA but that doesnt mean that it has got no future. Truly speechmaking the CDMA technology is the technology of the future. Gradually its gaining popularity in the European market.What is CDMA?CDMA (Code-Division Multiple Access) refers to any of several protocols employ in so-called second-generation (2G) and third-generation (3G) wireless communications. As the term implies, CDMA is a form of multiplexing, which furnishs numerous prefigures to occupy a single transmission television channel, optimizing the use of accessible spatewidth. The technology is used in ultra-high- frequence (UHF) cellular squall systems in the 800- megacycle and 1.9-GHz bands.CDMA employs parallel of latitude-to-digital conversion (ADC) in combination with facing pages spectrum technology. Audio scuttlebutt is first digitized into binary elements. The frequency of the transmitted signal is then feign to vary according to a defined pattern ( work out), so it john be intercepted only by a receiver whose frequency retort is programmed with the alike(p) cypher, so it follows exactly along with the transmitter frequency. There ar trillions of possible frequency-sequencing jurisprudences, which enhance privacy and makes cloning dif ficult.The CDMA channel is nominally 1.23 MHz wide. CDMA networks use a scheme called soft handoff, which minimizes signal breakup as a handset passes from one cell to an new(prenominal). The combination of digital and spread-spectrum modes supports several multiplication as to a greater extent than signals per unit bandwidth as analog modes. CDMA is matched with new(prenominal) cellular technologies this allows for nationwide roaming.The original CDMA mensuration, also cognise as CDMA One and still common in cellular tele call ups in the U.S., offers a transmission speed of only up to 14.4 Kbps in its single channel form and up to 115 Kbps in an eight-channel form. CDMA2000 and wideband CDMA deliver data many times cod-playinger.Code Division Multiple Access (CDMA) is a digital air interface standard, claiming eight to fifteen times the capacity of traditional analog cellular systems. It employs a commercial adaptation of a military spread-spectrum technology. Based on spre ad spectrum theory, it gives essentially the same services and qualities as wireline service. The primary difference is that admittance to the local anaesthetic exchange aircraft carrier (LEC) is reard via a wireless phone.Though CDMAs application in cellular phone is relatively new, it is not a new technology. CDMA has been used in many military applications, such asAnti-jamming (because of the spread signal, it is difficult to jam or interfere with a CDMA signal).Ranging (measuring the distance of the transmission to know when it entrust be received).Secure communications (the spread spectrum signal is very hard to detect).CDMA is a spread spectrum technology, which means that it spreads the information contained in a riveicular signal of interest over a much greater bandwidth than the original signal. With CDMA, unique digital codes, rather than separate RF frequencies or channels, argon used to differentiate subscribers. The codes be shargond by both the mobile situat ion (cellular phone) and the base station, and are called pseudo-random code sequences. Since each user is separated by a unique code, all users muckle share the same frequency band (range of radio spectrum). This gives many unique advantages to the CDMA technique over other RF techniques in cellular communication.CDMA is a digital multiple approach path technique and this cellular aspect of the protocol is specified by the Telecommunications patience tie-up (TIA) as IS-95. In CDMA, the BSSAP is divided into the DTAP and BSMAP (which corresponds to BSSMAP in GSM).Generating a CDMA signalThere are five steps in generating a CDMA signal.analog to digital conversionvocodingencoding and interleavingchannelizing the signalsconversion of the digital signal to a Radio Frequency (RF) signalThe use of codes is a key part of this process.How CDMA is altering the face of cellular and PCS communication?CDMA is altering the face of cellular and PCS communication byDramatically improving the telephone traffic capacityDramatically improving the voice quality and eliminating the audible effects of multipath attenuationReducing the incidence of dropped calls due to handoff failuresProviding reliable transport mechanism for data communications, such as facsimile and internet trafficReducing the number of spots needed to support any given amount of trafficSimplifying site selectionReducing deployment and operating costs because fewer cell sites are neededReducing average transmitted causationReducing contraceptive device to other electronic devicesReducing potential health risksCommercially introduced in 1995, CDMA quickly became one of the worlds fastest-growing wireless technologies. In 1999, the International Telecommunications Union selected CDMA as the industry standard for new third-generation (3G) wireless systems. Many leading wireless carriers are now building or upgrading to 3G CDMA networks in order to provide more capacity for voice traffic, along with high-sp eed data capabilities.CDMA is a form of Direct Sequence riddle Spectrum communications. In general, Spread Spectrum communications is distinguished by three key elementsThe signal occupies a bandwidth much greater than that which is necessary to send the information. This results in many benefits, such as immunity to interference and jamming and multi-user access, which well discuss later on.The bandwidth is spread by means of a code which is independent of the data. The independence of the code distinguishes this from standard modulation schemes in which the data modulation will unceasingly spread the spectrum somewhat.The receiver synchronizes to the code to recover the data. The use of an independent code and synchronous reception allows multiple users to access the same frequency band at the same time.In order to protect the signal, the code used is pseudo-random. It appears random, but is actually deterministic, so that the receiver rout out reconstruct the code for synchron ous detection. This pseudo-random code is also called pseudo-noise (PN).There are three ship canal to spread the bandwidth of the signalFrequency hopping. The signal is quick switched between different frequencies indoors the hopping bandwidth pseudo-randomly, and the receiver knows before hand where to find the signal at any given time.Time hopping. The signal is transmitted in piffling bursts pseudo-randomly, and the receiver knows beforehand when to expect the burst.Direct sequence. The digital data is at present coded at a much higher frequency. The code is fixd pseudo-randomly, the receiver knows how to generate the same code, and correlates the received signal with that code to extract the data.HOW SPREAD SPECTRUM full treatment?Spread Spectrum uses wide band, noise-like signals. Because Spread Spectrum signals are noise-like, they are hard to detect. Spread Spectrum signals are also hard to Intercept or demodulate. Further, Spread Spectrum signals are harder to jam (int erfere with) than narrowband signals. These Low Probability of Intercept (LPI) and anti-jam (AJ) features are why the military has used Spread Spectrum for so many years. Spread signals are deliberately made to be much wider band than the information they are carrying to make them more noise-like.Spread Spectrum signals use fast codes that run many times the information bandwidth or data rate. These special Spreading codes are called malingerer Random or Pseudo Noise codes. They are called Pseudo because they are not real Gaussian noise.Spread Spectrum transmitters uses similar transmit power levels to narrow band transmitters. Because Spread Spectrum signals are so wide, they transmit at a much lower spectral power density, measured in Watts per Hertz, than narrowband transmitters. This lower transmitted power density characteristic gives spread signals a big plus. Spread and narrow band signals can occupy the same band, with little or no interference. This capability is the main reason for all the interest in Spread Spectrum today.IMPLEMENTATION OF CDMA TECHNOLOGYNow a day, in large organization the communication process has to be fast and efficient. There are the study points that have to be taken wish in the modern corporate culture. Over time, more and more demands have been made on the capabilities of corporate networks. Workers want more mobility secure, high-speed access and an extension of applications across the enterprise, all of which can strain current IT capabilities. The first and fore or so of all is protecting corporate network assets is an ongoing parturiency for IT professionals. Increased worker mobility and mobile workers needs for immediate, secure access to captious business information add challenges to maintaining network securitySome of todays illuminate security issues and concerns areUnauthorized systems and network accessAuditability and compliance guest data breachesInternal and external sabotageTheft of intellectual propo rtion and confidential business informationCost of mobile device plaqueThe following diagram illustrates many elements critical to mobile data security. leaving BETWEEN GSM AND CDMA TECHNOLOGYIn cellular service there are two main competing network technologies Global System for Mobile communication theory (GSM) and Code Division Multiple Access (CDMA). Cellular carriers including Sprint PCS, Cingular Wireless, Verizon and T-Mobile use one or the other. Understanding the difference between GSM and CDMA will allow you to choose a carrier that uses the preferable network technology for your needs.The GSM Association is an international organization founded in 1987, dedicated to providing, developing, and overseeing the worldwide wireless standard of GSM. CDMA, a proprietary standard designed by Qualcomm in the get together States, has been the dominant network standard for North America and parts of Asia. However, GSM networks handle to make inroads in the joined States, as CDMA n etworks make progress in other parts of the world. There are camps on both sides that unwaveringly believe either GSM or CDMA architecture is superior to the other. That said, to the non-invested consumer who simply wants back end line information to make a choice, the following considerations may be helpful.CoverageThe most important factor is getting service in the areas you will be using your phone. Upon viewing competitors coverage maps you may go that only GSM or CDMA carriers offer cellular service in your area. If so, there is no decision to be made, but most people will find that they do have a choice.Data Transfer furtherWith the advent of cellular phones doing double and triple duty as blow video devices, podcast receivers and email devices, speed is important to those who use the phone for more than making calls. CDMA has been traditionally faster than GSM, though both technologies continue to rapidly leapfrog along this path. Both boast 3G standards, or 3rd generatio n technologies.EVDO, also known as CDMA2000, is CDMAs answer to the need for speed with a downstream rate of about 2 megabits per second, though some reports apprize real world speeds are nearer to 300-700 kilobits per second (kbps). This is comparable to introductory DSL. As of fall 2005, EVDO is in the process of being deployed. It is not available everywhere and hires a phone that is CDMA2000 ready.GSMs answer is pass on (Enhanced Data rate for GSM Evolution), which boasts data rates of up to 384 kbps with real world speeds reported closer to 70-140 kbps. With added technologies still in the works that include UMTS (Universal Mobile Telephone Standard) and HSDPA (High renovate Downlink Packet Access), speeds reportedly increase to about 275380 kbps. This technology is also known as W-CDMA, but is incompatible with CDMA networks. An EDGE-ready phone is required.In the case of EVDO, suppositional high traffic can degrade speed and performance, bandage the EDGE network is mo re susceptible to interference. Both require being within close range of a cell to get the best speeds, while performance decreases with distance.Subscriber Identity Module (SIM) cardsIn the United States only GSM phones use SIM cards. The removable SIM card allows phones to be instantly activated, interchanged, swapped out and upgraded, all without carrier intervention. The SIM itself is tied to the network, rather than the actual phone. Phones that are card-enabled can be used with any GSM carrier.The CDMA equivalent, a R-UIM card, is only available in parts of Asia but remains on the horizon for the U.S. market. CDMA carriers in the U.S. require proprietary handsets that are linked to one carrier only and are not card-enabled. To upgrade a CDMA phone, the carrier must deactivate the honest-to-goodness phone then activate the new one. The old phone becomes useless.RoamingFor the most part, both networks have fairly concentrated coverage in major cities and along major highways. G SM carriers, however, have roaming contracts with other GSM carriers, allowing wider coverage of more plain areas, generally speaking, often without roaming charges to the customer. CDMA networks may not cover rural areas as well as GSM carriers, and though they may contract with GSM cells for roaming in more rural areas, the charge to the customer will generally be significantly higher.International RoamingIf you need to make calls to other countries, a GSM carrier can offer international roaming, as GSM networks dominate the world market. If you travel to other countries you can even use your GSM cell phone abroad, providing it is a quad-band phone (850/900/1800/1900 MHz). By purchasing a SIM card with minutes and a local number in the country you are visiting, you can make calls against the card to save yourself international roaming charges from your carrier back home. CDMA phones that are not card-enabled do not have this capability, however there are several countries that u se CDMA networks. Check with your CDMA provider for your specific requirements.According, CDMA networks support over 270 cardinal subscribers worldwide, while tallies up their score at over 1 billion. As CDMA phones become R-UIM enabled and roaming contracts between networks improve, integration of the standards might eventually make differences all but transparent to the consumer.The chief GSM carriers in the United States are Cingular Wireless, of late merged with ATT Wireless, and T-Mobile USA. Major CDMA carriers are Sprint PCS, Verizon and Virgin Mobile. There are also several smaller cellular companies on both networks.

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