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Wireless communication Video Lecture information

http://nptel.iitm.ac.in/video.php?subjectId=117102062

Which technology is better?

Introduction :

Before deciding which technology is superior.let's talk a little more about these two technologies:

• CDMA: stands for code Division Multiple Access.Both data and voice are separated from signals using codes and then transmitted using a wide frequency range.Because of this.there are more space left for data transfer(this was one of the reasons why CDMA is the preferred technology for  the 3G generation which is broadband access and the use of big multimedia messages).14% of the worldwide market goes to CDMA. For the 3G generation CDMA uses 1x EV-DO and EV-DV. It was a lot of users in asia,specially in south korea.
• GSM: stands for Global system mobile .Even though it is sold as"the latest technology" in several countries ,this technology is older than CDMA( and also TDMA). But keep in mind that this doesn't means that GSM is inferior or worse than CDMA.Roaming readiness and fraud prevention are two major advantages from this technology. GSM is the most used cell phone technology in the world,with 73% of the worldwide market. It has a very strong presence in Europe.

TDMA technology is the less used from the three main digital technologies(GSM,CDMA,TDMA) and we think it will gradually be replaced to CDMA or GSM. That's why the GSM vs CDMA war. At one corner,GSM operators say it is better" because it uses a SIM chip,it is the most used technology worldwide ,it is more secure and it is more advanced".On the other corner, CDMA follows say it is better "because it is the 3G generation chosen technology and GSM will migrate to CDMA since CDMA is more advanced..."

y to describe the war between 

But which one of these staements are correct? Acordingly to nokia, "this discussion is not about technology anymore,but about market". We think this is the best way to describe the war between these two cell phone technologies.

In the beginning, GSM was in fact superior. It had more services and allowed more data transfer. But CDMAA,facing the advantages of the competitor standard,soon delivered the same features found on GSM now a days. it is not possible to say that GSM services are better than CDMA. Miltimedia messages,video,high-speed internet access,digital camera and even PDA function are some of the features we can found on both technologies. The new CDMA 1xRTT technology, which previews what G3 cell phones will bring,is more advanced than EDGE, technology from the beginning of 3G generation.allowing higher transfer rates.

Even the GSM SIM card advantages,that allows you to change your cell phone and keep your phone list, is being surplussed by some CDMA operators with a service that allows you to store your phone book on the operator's database,allowing you to recover your phone book even if your cell phone is stolen(which is not possible with GSM, since if your cell phone is stolen ,your sim card will be stolen together). Noties that recently a new accessory called SIM backup was released,which allows you to backup the data stored in your SIM sard.Also some GSM operators are offering a similar backup service.
So, nowadays both technologies are equiparated in technology, but this picture won't be like that in the future. Afterall, CDMA evolution ground is wider and in a few years it will be superior than GSM. This means that GSM operators will disapear? Not at all. They will migrate over CDMA and the war will continue, because the existing CDMA operators chose to use 1xEV-DO and1XEV-DV technologies for their 3G network and the existing GSM operators have opted for a different technology, called WCDMA. Also, even though the current GSM operators will migrate to WCDMA, they still can use their existing GSM network. So users won't feel anything special when the operators shift to the new cell generation (3G), independently from the technology they choose.

Difference between CDMA and GSM

Ans1. 
Difference between CDMA & GSM- 
These are the two different means of mobile communication being presently used world wide. The basic difference lies in the Multiplexing method used in the airial communication i.e. from Mobile Tower to your mobile and vice versa...

CDMA uses Code Division Multiple Assess as the name itself indicates, for example you are in a hall occupied with number of people speaking different language. You will find that the one language you are knowing will be heard by you and the others will be treated like noise. In the same manner each CDMA mobile communication takes place with a "code" communicating between them and the other end if one is knowing that code then only it can listen to the data being transmitted i.e. the communication is in the coded form.

On the other hand GSM uses Frequency Division Multiplexing in which each user is allocated a particular bandwidth till the communication is taking place.

Ans 2. About the sim card....
CDMA handsets do not use SIM cards. The handset is assigned a number from the telecom operator and get incorporated in itself. CDMA handset have RSN number which gets linked to a specific number assigned by operator.
Ans 4. full form of GSM & CDMA.
GSM - Global System for Mobile communication.
CDMA - Code Division Multiple Access

Another Answer::::

gsm is stands for global system for mobile communication. it use tdma & fdma techniques as access mechanism . in gsm we devide bandwidth in to time slots for better utilization of bandwidth.cdma stands for code devision muliple access it use cdma techniques as access mechanism . in cdma we allocate a unique code for every user saparately and allocate bandwidth to user

Answer:::::

The main difference between GSM and CDMA is: In GSM, the entire frequency band is not available to the end-user, while in CDMA the entire frequency band is available to the end-user. So, the Frequency Re-use factor is 1 in CDMA. 

GSM Works as follows:
---------------------
     The entire frequency band is divided into chunks and each such chunk is divided into timeslots and each such portion is made available to a user. 

CDMA Works as follows:
-----------------------
    The entire frequency band is available to the user. So, in order to differentiate, the transmission from each user is "spread" or coded using an unique code given to individual user. At the receiving end, the spread information is decoded.
Answer:
GSM is a Global Syatem For Mobile Communication.GSM Operates 3 bands, 1) GSM 900 2) GSM 1800 and 3) GSM 1900. GSM 900 & GSM 1800 are used in india, But, GSM 1900 used in USA.GSM and CDMA techniques can be explained with an example,suppose there are 10 persons in a room and they want to communicate with each other .How can they communicate? First method:One persons speaks at one time that means we
have provided a definite time interval to that person.-GSM Second method :all the peers  speak at a time in a different language which we call as CDMA
CDMA stands for Code Division Multiple Access and GSM  stands for Global system for Mobile Communication.  In CDMA phones the software is integral with the phone 
instrument and in the case of GSM phones it is through the 
SIM Card.

CDMA phone instruments are dedicated to the service  provider. GSM phone instruments are portable across service providers through SIM cards.
Answer:::::::::::::

GSM: In GSM only 30 or 35 peoples can call at at time in a  singal carrier but InCDMA apprx 70 peoples can call in a  singal carrier at a time


Answer:::
gsm is stand by globle system for mobile communication,gsm frequency band is 900mhz-1800mhz,this is communicate all rural area in all time,cdma is same frequency band but can not available in rural area in all time.

Q. What is the meaning of C.D.M.A & G.S.M. TECHNOLOGY, & IT'S FULL FORM

1.N cellular service there are two main competing network technologies: Global System for Mobile Communications (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 United States, has been the dominant network standard for North America and parts of Asia. However, GSM networks continue to make inroads in the United States, as CDMA networks make progress in other parts of the world. There are camps on both sides that firmly believe either GSM or CDMA architecture is superior to the other.

2.Gsm means all sim support this mobile & cdma means only particular singal company sim supported

3.In Mobile, what is the mean of CDMA & GSM

4.GSM

In 1989, GSM responsibility was transferred to the European Telecommunication Standards Institute (ETSI), and phase I of the GSM specifications were published in 1990. Commercial service was started in mid1991, and by 1993 there were 36 GSM networks in 22 countries, with 25 additional countries having already selected or considering GSM In addition to Europe, South Africa, Australia, and many Middle and Far East countries have chosen to adopt GSM. By the beginning of 1994, there were 1.3 million subscribers worldwide. The acronym GSM now (aptly) stands for Global System for Mobile telecommunications.

From the beginning, the planners of GSM wanted ISDN compatibility in services offered and control signaling used. The radio link imposed some limitations, however, since the standard ISDN bit rate of 64 Kbps could not be practically achieved.

The digital nature of GSM allows data, both synchronous and asynchronous data, to be transported as a bearer service to or from an ISDN terminal. The data rates supported by GSM are 300 bps, 600 bps, 1200 bps, 2400 bps, and 9600 bps.

The most basic teleservice supported by GSM is telephony. A unique feature of GSM compared to older analog systems is the Short Message Service (SMS). Supplementary services are provided on top of teleservices or bearer services, and include features such as international roaming, caller identification, call forwarding, call waiting, multiparty conversations, and barring of outgoing (international) calls, among others.



CDMA

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 spread spectrum theory, it gives essentially the same services and qualities as wireline service. The primary difference is that access to the local exchange carrier (LEC) is provided via a wireless phone.

Though CDMAs application in cellular telephony is relatively new, it is not a new technology. CDMA has been used in many military applications, such as:

* Anti-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 will 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 particular signal of interest over a much greater bandwidth than the original signal. With CDMA, unique digital codes, rather than separate RF frequencies or channels, are used to differentiate subscribers. The codes are shared by both the mobile station (cellular phone) and the base station, and are called pseudo-random code sequences. Since each user is separated by a unique code, all users can 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 access technique and this cellular aspect of the protocol is specified by the Telecommunications Industry Association (TIA) as IS-95. In CDMA, the BSSAP is divided into the DTAP and BSMAP (which corresponds to BSSMAP in GSM)

CDMA vs GSM

GSM and CDMA are competing wireless technologies with GSM enjoying about an 82% market share globally. In the U.S., however, CDMA is the more dominant standard. Technically GSM (Global System for Mobilecommunications, originally from Groupe Spécial Mobile) is a specification of an entire wireless network infrastructure, while CDMA relates only to the air interface — the radio portion of the technology.

Code division multiple access (CDMA) describes a communication channel access principle that employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code). CDMA also refers to digital cellular telephony systems that use this multiple access scheme, as pioneered by QUALCOMM, and W-CDMA by the International Telecommunication Union (ITU), which is used in GSM’s UMTS

For more visit 

http://www.diffen.com/difference/CDMA_vs_GSM

What Is the Difference Between GSM and CDMA?

Global System for Mobile Communications (GSM) and Code Division Multiple Access (CDMA) are two competing standards in cellular service. They both have derivatives for use with 3Gphones known as Universal Mobile Telecommunications System (UMTS) and CDMA2000, respectively. The major difference between the two technologies is how they turn voice data into radio waves and how the carrier connects to the phone. Other differences include the coverage area, the data transfer speeds, and the type of hardware used.

Coverage

Some areas and countries only have one technology available, so users should be sure to review coverage maps before buying a phone. Generally speaking, CDMA is most commonly found in North America and some parts of Asia, while GSM is found in most other places. Some carriers do offer international or "world" phones that can work with both, but if the phone is going to be used predominantly in one area, it may make sense just to get one that's tied to one type.

Data Transfer Speed

Both technologies can be used with 3G standard phones, but 3G GSM speeds can be faster than 3G CDMA speeds, which can make a big difference for those who use their phones for social networking, email and streaming video. The fastest 3G standard used with CDMA2000 isEV-DO Rev B., which has downstream data rates of about 15.67 Megabits per second (Mbit/s). The fastest standard available with UMTS is HSPA+, with downstream speeds of up to 28 Mbit/s.

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Hardware

GSM phones and CDMA phones also use different types of smart cards known as Universal Integrated Circuit Cards (UICC). These are small removable cards that can be used to store information like a contact list and activate, interchange, and upgrade phones without carrier intervention as long as the phone is unlocked. This means that the carrier makes it possible for phone to work even if the end user removes and changes the card. Though both types can be sold locked, this is more common with CDMA phones.

UICCs can be programmed to work with either GSM or CDMA and their derivatives, or with both. Those that only work with GSM phones are called Subscriber Identity Module (SIM) cards and those that only work with CDMA phones are called CDMA2000 Subscriber Identity Module (CSIM) cards. There are also a few types of UICCs that are programmed to work with GSM, UMTS, CDMA, and CDMA2000, including CSIM/USIM cards and Removable User Identity Module (R-UIM) cards.

Roaming

Generally speaking, both networks have fairly concentrated coverage in major cities and along major highways. GSM carriers, however, have roaming contracts with other GSM carriers, allowing wider coverage of more rural areas, generally speaking, often without roaming charges to the customer. CDMA networks may not cover rural areas as well, and though they may contract with GSM cells for roaming in more rural areas, the charge to the customer can be significantly higher.

International Roaming

Some GSM and CDMA carriers offer international roaming, which means users can still use their phones when traveling abroad. To work internationally, the phone has to be a quad-band phone, which means that it works with frequencies of 850, 900, 1800, and 1900 MHz. Additionally, the phone does have to be unlocked and the user does have to be trying to use a network that exists in the country, which is sometimes more difficult to do with CDMA since fewer countries have CDMA networks. If the phone is unlocked and there is a network present, though, then users can buy a UICC with minutes and a local number in the country in which they're traveling to avoid paying international rates.

4G

The distinction between the two technologies is largely irrelevant in 4G phones, since both can be used with the both of the main standards used with 4G phones, Long Term Evolution (LTE) and Worldwide Interoperability for Microwave Access (WiMax). Since GSM and CDMA work by means to radio waves, but 4G technologies work by means of an IP network, the radio signals from both have to be translated into electronic data for use on the network or the phone has to switch back to a 2G or 3G network to make voice calls.

GSM and CDMA

What do "GSM" and "CDMA" mean in terms of cell phone service?

...

They are communication standards

I guess I needed to elaborate in my answer about K1 phones. Well, I'll do it here. GSM and CDMA are two different communication standards. All U.S. providers use exclusively one or the other. GSM means "Global System for Mobile communications", and it is the standard currently in use more or less worldwide. In the U.S., the major providers using this standard are T-Mobile and AT&T Wireless. CDMA means "Code Division Multiple Access". This standard used to be the dominant standard in the U.S. Now it is used by Verizon and Sprint. It still has more users than GSM, but the difference is not very significant.   Historically, CDMA was developed by Qualcomm, made a U.S. standard, and gained some acceptance before GSM became established; however, once GSM was created, all countries without established CDMA networks accepted GSM - this is the reason why CDMA is almost non-existent anywhere but USA and Japan. From a user's point of view, the actual standard is not really important, with two caveats: first, you can't use a phone that uses one standard with the provider that uses the other standard; second, if you travel internationally, a GSM phone is almost a must.

What is Diac?

The DIAC is a bidirectional trigger diode designed  to trigger a Triac or SCR. The Diac
like the four-layered diode remains non-conducting  until its ‘break-over voltage’ is
reached. At this point, it turns on fully and remains on until the applied voltage or circuit
current is reduced below the ‘holding values’. The basic action of a diac is that, when
connected across a voltage source with a current limiting resistor, it act like a ‘high
impedance’ till the applied voltage rises to above 35 volts. Then the diac act as a 30 volt
Zener diode and conducts. The remaining 5 volts develop across the current limiting
resistor. At the avalanche state, diac exhibits ‘negative resistance characteristics’ and the
voltage across it ‘snaps back’ typically about 5 volts sufficient to trigger the Triac or
SCR. If the forward current falls below the minimum holding value of 30 volts (typical),
diac will turn off. The important draw back of the device is that, it cannot be triggered at
just any point in the AC power cycle. It triggers at its preset break over voltage only.

Diacs are used in AC power control circuits to provide trigger pulse to Triacs for its
proper operation.

During each half cycle of waveform, capacitor C1 charges depending on the value of R1.
When the voltage in the capacitor rises to the break down voltage of diac, it will conduct
sending a positive pulse to the gate of triac. The triac and lamp then turns on and remains
in the’ On state’ until the waveform crosses through zero voltage again