nikesh cdma

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Code division multiple accessCDMA

NIKESH MURJANI

&RUPESH KUMAR1ST YEAR.B.TECH.

INDIAN SCHOOL OF MINES,DHANBAD



Any sufficiently advanced technology is Any sufficiently advanced technology is

indistinguishableindistinguishable from magic.from magic.--Source UnknownSource Unknown



WHAT IS CDMA?

Code division multiple access (CDMA ) describes acommunication channel access principle that employs spread-spectrum technology and a special coding scheme (where eachtransmitter is assigned a code ). In communications technology,there are only three domains that can allow multiplexing to beimplemented for more efficient use of the available channelbandwidth and these domains are known as time, frequency andspace. CDMA divides the access in signal space. By contrast,time division multiple access (TDMA) divides access by time ,

while frequency-division multiple access (FDMA ) divides it byfrequency . CDMA is a form of "spread-spectrum" signaling, sincethe modulated coded signal has a much higher bandwidth thanthe data being communicated.



W HAT IS SPREAD SPECTRUM?

CDMA is a form of Direct Sequence Spread Spectrumcommunications. In general, Spread Spectrumcommunications is distinguished by three key elements:1. The signal occupies a bandwidth much greater than thatwhich is necessary to send the information. This results in

many benefits, such as immunity to interference and jamming and multi-user access, which we¶ll discuss later on.2. The bandwidth is spread by means of a code which isindependent of the data. The independence of the codedistinguishes this from standard modulation schemes inwhich the data modulation will always spread the spectrumsomewhat.3. The receiver synchronizes to the code to recover the data.The use of an independent code and synchronous receptionallows multiple users to access the same frequency band atthe same time.



RELAIBILITY OF CDMA



G SM VS. CDMAThe G SM Association is an international organizationfounded in 1987, dedicated to providing, developing, andoverseeing the worldwide wireless standard of G SM. CDMA,a proprietary standard designed by Qualcomm in the United

States, has been the dominant network standard for North America and parts of Asia. However, G SM networkscontinue to make inroads in the United States, as CDMAnetworks make progress in other parts of the world. Thereare camps on both sides that firmly believe either G SM or CDMA architecture is superior to the other. That said, to thenon-invested consumer who simply wants bottom lineinformation to make a choice, the following considerationsmay be helpful





CDMA MODEM



W HAT A BASIC UNIT SHOULDCHECK BEFORE SELECTIN G ASERVICE

Coverage : The most important factor is getting service in theareas you will be using your phone. Upon viewing competitors'coverage maps you may discover that only G SM or CDMA carriersoffer cellular service in your area. If so, there is no decision to bemade, but most people will find that they do have a choice.

Data Transfer Speed : W ith the advent of cellular phones doing double and triple duty as streaming video devices,

podcast receivers and email devices, speed is important to thosewho use the phone for more than making calls. CDMA has beentraditionally faster than G SM, though both technologies continue torapidly leapfrog along this path. Both boast "3 G " standards, or 3rdgeneration technologies.



CDMA AT DIFFERENT PLACES



Subscriber Identity Module (SIM) cards : In the UnitedStates only G SM phones use SIM cards . The removable SIMcard 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 actualphone. Phones that are card-enabled can be used with anyG SM carrier.The CDMA equivalent, a R-UIM card, is only available inparts of Asia but remains on the horizon for the U.S. market.CDMA carriers in the U.S. require proprietary handsets thatare linked to one carrier only and are not card-enabled. Toupgrade a CDMA phone, the carrier must deactivate the old

phone then activate the new one. The old phone becomesuseless



Roaming : For the most part, bothnetworks have fairly concentrated coverage inmajor cities and along major highways. G SMcarriers, however, have roaming contracts withother G SM carriers, allowing wider coverage of more rural areas, generally speaking, often withoutroaming charges to the customer. CDMA networksmay not cover rural areas as well as G SM carriers,and though they may contract with G SM cells for roaming in more rural areas, the charge to thecustomer will generally be significantly higher.





International Roaming : If you need tomake calls to other countries, a G SM carrier canoffer international roaming, as G SM networksdominate the world market. If you travel to other

countries you can even use your G

SM cell phoneabroad, providing it is a quad-band phone(850/900/1800/1900 MHz ). By purchasing a SIMcard with minutes and a local number in thecountry you are visiting, you can make callsagainst the card to save yourself international

roaming charges from your carrier back home.CDMA phones that are not card-enabled do nothave this capability, however there are severalcountries that use CDMA networks. Check withyour CDMA provider for your specific requirements



The CDMA community is aggressively targeting technology based onmobile diversity antennas, a handset-based smart antenna methodologythat requires no network modifications but will increase capacity by a factor of two. The idea behind this approach is to combine signals from twoseparate antennas to reduce the impact of spatial variations in signalstrength and thus increase the average data rate available. Mobile diversityantennas can also be used when one needs to put antennas for two unlikeservices - for instance CDMA for voice and data and G PS for tracking - intoa single device.

Mobile diversity solutions can be used alone or in combination with smartantennas in the network infrastructure to provide even more impressivecapacity gains and improved customer satisfaction through better overallvoice and data call performance. Network smart antennas, which do notrequire any changes to end-user mobile devices, can be embedded in base

stations or added to existing networks as appliqué solutions. Such antennascan be deployed on a per-cell-site or per-sector basis in order to alleviatespecific or localized capacity issues. Both large and small vendors offer smart antennas for the CDMA marketplace.Presentations



MOBILE LOVE IN INDIAFile this under asinine and absurd along with thecellphone throwing contest : Deepak Sharma wenton record with the G uinness Book for having sentthe most SMS messages in a single month:182,689. W e're not sure if that's total, or uniquemessages, but if you'd like us to break that downfor you, that's about 6,100 messages a day, 253an hour, 4.2 a minute, or a new one every 14seconds or so. So basically this guy gave up amonth of his life sending texts²way to go, dude.His other reward? A 1,411 page bill (don't worry,

he has an unlimited texting plan )²compare thatto, say, Joyce's Ulysses (speaking of G uinnessbooks« aw come on! ), which is a mere 780 some-odd pages, though every bit as difficult to readthrough.www.engadget.com



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nikesh cdma