GSM vs CDMA

Discussion in 'Wireless & RF Design' started by sharma2k7, Jun 6, 2008.

  1. sharma2k7

    Thread Starter Active Member

    Dec 10, 2007
    36
    0
    Hi Everybody,

    What's is the advantage with one over another in CDMA & GSM technologies
     
  2. Tommy_cs

    New Member

    Sep 25, 2005
    3
    0
    I think GSM is more common in the world as it is cheap and flexible.

    As I know, we can swap GSM provider by swapping GSM sim cards but for CDMA,there are no such cards..so the phone must registered with the provider. ( I am not 100% sure )

    and both CDMA and GSM support voice and data, they are more or less the same from user's point of view.
     
  3. Reshma

    Active Member

    Mar 11, 2007
    54
    0
  4. silencer

    New Member

    Jun 3, 2008
    9
    0
    The basic schemes for these two multiple access schemes are fundamentally very different.

    GSM uses time-division to facilitate reuse of the channels. Thus, when initiating a call, a user would be assigned (by the base-station) a particular time interval during which it is permitted to transmit. This would be happening over a number of different sub-carriers, each a supporting a certain number of users.

    CDMA uses a spread-spectrum technique to allow multiple access via code-division. In this case, every user in the cell transmits all the time, over the same channel. The elegance of the spread-spectrum technique is that each user modulates its information using a different code. When a user initiates a call, the base station will assign it a unique code, also called a chipping sequence, which is a pseudo-random code of a particular length. Modulating the transmit waveform by this sequence is akin to stamping each waveform with its own unique label. The process of modulating the waveform spreads the spectrum of the transmitted signal. In doing so, the spectrum often drops below the noise floor, and is thus apparently indistinguishable from noise and other users in the same area (thus making it useful for undetectable communication). The original signal is recovered by correlating the signal with the known chipping sequence.

    Of coures, both techniques have their advantages and disadvantages, which we can discuss if others are interested.
     
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