The mobile industry in India is divided between the two technologies GSM and CDMA. While the earlier service providers had adopted the GSM technology, the new players have been using CDMA technology and have notched up a significant share of the Indian market. Hence any discussion on Mobile Forensics needs to take into account the presence of the two technologies.
It is necessary for us to understand the basic differentiation of the two technologies as they may have an impact on the Forensics. An attempt is made here to present the fundamental technical aspects about the two systems.
GSM stands for Global System for Mobile Communications and CDMA stands for Code Division Multiple Access. They represent different systems of sharing of the radio spectrum for communication.
Normally the radio spectrum can be shared by different users accessing the same frequency band without causing interference. The techniques used for this are TDMA (Time division multiple access), FDMA (Frequency division multiple access) and CDMA (Code division multiple access).
GSM (Global System for Mobile Communications) is a form of multiplexing, which divides the available bandwidth among the different channels.
[...] 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 1.9 GHz) bands in North America and Latin America. [...]
[...] On the other corner, CDMA followers say it is better "because it is the 3G generation chosen technology and GSM will migrate to CDMA since CDMA is more advanced . " But which one of these statements are correct? Accordingly 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. [...]
[...] You can move the SIM (subscriber identity module) of a GSM-based phone to any other GSM-based phone, making GSM the optimal choice for international travelers who need connectivity. You can find dual-mode and tri-mode phones, but before you buy, check to see whichmodes the phone actually connects. The term can be deceptive. In most cases it will mean that a handset can support two digital technologies, such as CDMA and TDMA, as well as analog. In this case the handset is considered to be a true tri-mode phone. [...]
[...] 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 old phone then activate the new one. The old phone becomes useless. Roaming: For the most part, both networks have fairly concentrated coverage in major cities and along major highways. [...]
[...] The modulation used in GSM is Gaussian minimum shift keying (GMSK), a kind of continuous-phase frequency shift keying. In GMSK, the signal to be modulated onto the carrier is first smoothened with a Gaussian low- pass filter prior to being fed to a frequency modulator, which greatly reduces the interference to neighboring channels (adjacent channel interference. Network structure GSM NETWORK STRUCTURE The network behind the GSM system seen by the customer is large and complicated in order to provide all of the services which are required. [...]
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