GSM is a form of multiplexing, which divides the available bandwidth among the different channels. Most of the times th...
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Prepared By: Md. Moshiur Rahman Khan Email: [email protected]
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GSM and CDMA have following differences The GSM stands for global system for mobile communication and CDMA for code division multiple accesses. GSM is a form of multiplexing, which divides the available bandwidth among the different channels. Most of the times the multiplexing used are either TDM (Time division multiplexing) or FDM (Frequency division multiplexing). On the other hand CDMA is a type of multiple access scheme (which means allotting the given bandwidth to multiple users) and makes use of spread spectrum technique which is essentially increasing the size of spectrum. In CDMA each user is provided a unique code and all the conversation between 2 users are coded. This provides a greater level of security to CDMA users than the GSM ones.
Example : We can understand the basic difference between CDMA and GSM with the following example. Suppose there is a big room in which there are 10 couples who wish to talk but in way that they are not disturbed. There are 3 ways of doing this Only one couple stay in the room and rest 9 leave it for a while, say 5 minutes. For those 5 minutes that couple can talk with each other and at the end of that it will go out and the next couple will come. At the end of the time slot of 10th couple, the 1st couple will come back to continue its conversation and the cycle would continue. This is analogous to TDMA (Time division Multiple access) a technique derived from TDM. Another way is to divide the area of the room in 10 equal parts and then ask these couples to stay within their respective areas and talk. This is analogous to FDMA, a technique derived from FDM. Finally the couples can be allowed to stand anywhere in the room and converse. They need not wait to get their time slot or be confined in a particular place. The only condition now is that all of them must speak in different languages. This is analogous to CDMA technique. Page | 2
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. GSM is the “branded” term referring to a particular use of TDMA (Time-Division Multiple Access) technology. GSM is the dominant technology used around the globe and is available in more than 100 countries. It is the standard for communication for most of Asia and Europe. GSM operates on four separate frequencies: You’ll find the 900MHz and 1,800MHz bands in Europe and Asia and the 850MHz and 1,900MHz (sometimes referred to as 1.9GHz) bands in North America and Latin America. GSM allows for eight simultaneous calls on the same radio frequency and uses “narrowband” TDMA, the technology that enables digital transmissions between a mobile phone and a base station. With TDMA the frequency band is divided into multiple channels which are then stacked together into a single stream, hence the term narrowband. This technology allows several callers to share the same channel at the same time. CDMA takes an entirely different approach from GSM/TDMA. CDMA spreads data out over the channel after the channel is digitized. Multiple calls can then be overlaid on top of one another across the entire channel, with each assigned its own “sequence code” to keep the signal distinct. CDMA offers more efficient use of an analog transmission because it allows greater frequency reuse, as well as increasing battery life, improving the rate of dropped calls, and offering far greater security than GSM/TDMA. For this reason CDMA has strong support from experts who favor widespread development of CDMA networks across the globe. Currently, you will find CDMA mostly in the United States, Canada, and North and South Korea. (As an interesting aside, CDMA was actually invented for the military during World War II for field communications.) I hope it will help you to understand these technologies.
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What is the main difference between GSM & CDMA? Ans 1: GSM is global system for mobile communication. It uses FDMA & TDMA as access mechanism. In GSM we divide bandwidth in to time slots for better utilization of bandwidth. CDMA - it stands for code division multiple access. In CDMA we allocate a unique code for every user separately and allocate bandwidth to user.
Ans 2: 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 enduser. 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 a unique code given to individual user. At the receiving end, the spread information is decoded.
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