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GSM vs WCDMA

Discussion in 'GENERAL Wireless Discussion' started by Maximinfo, Feb 25, 2003.

  1. Maximinfo

    Maximinfo New Member

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    I am searching information about difference between GSM and WCDMA systems. I have noticed that lots of information is shared here and i decided to join. So what i need is i have to find exact information about GSM WCDMA systems so i can compare them and find the difference between them. If you want to search it from the internet you find that there is million places with all kinds of information, so any kind help from you is needed. I just entered this site so i do not know all the rules around here but maybe i am allowed to ask something like this.

    Thanks for advance.
     
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  2. northform

    northform Bronze Senior Member
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    wCDMA is the third generation GSM technology. It isn't available now, except in Japan. It will be comparable to 1xEV-DO/DV from Qualcomm. GSM/GPRS is the 2.5G technology equivalent to Qualcomm's 1xRTT. Both GSM and wCDMA use the same codecs and a lot of the same technology. The biggest difference between the two is that the air interface has changed from a time/frequency division to a code division. Is there something specific that you want to know? Like will wCDMA have a greater call capacity/higher data rates/better sound quality? Those answers are yes/yes, but not much higher than EDGE/depends on whether the carrier uses the extra capacity to let their customers use the EFR codec or whether they will have everyone use the AMR codec so that they can offer more minutes to customers. GSM phones today are capable of both and which one your phone uses depends on how full the network is. It will be the same way with wCDMA.
     
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  3. Maximinfo

    Maximinfo New Member

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    I am familiar with greater call capacity and higher data rates but better sound quality? What makes it better? Is there something doing with receiver in WCDMA? That it receives signals from many sources and signal becomes more powerfull. RAKE-receiver i think. Do you have any specific info from that? Handover in WCDMA is also a bit tricky.. The phone makes connection to another cell before it disconnects from first cell. I would have so many questions but maybe you have time to answer these. Thanks again.
     
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  4. northform

    northform Bronze Senior Member
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    A rake antenna doesn't transmit (or recieve) to more than one tower at a time. Basically, it uses off-sets of a common spreading code to receive and combine several multipath signals. In English that basicly means that the phone transmits the same signal multiple time and receives the same signal multiple times from/to the same tower so that if one piece gets broken up, there is redundance to make sure that you don't notice. It would be like someone repeating everything that they say to you. Even if you missed it the first time, one of the further times would give you the message.

    wCDMA does connect to a new tower before the handoff, but the new tower doesn't begin to handle the call (ie. transmit the person you are calling to you or you to the person you are calling) until the old connection is terminated. The same goes for Qualcomm's CDMA. GSM currently scans and tests for new towers. All that a soft handoff does is prevent a split second gap between when the phone disconnects from one tower and connects to the new one. It isn't more reliable.

    Sound quality is more determanant on codecs than on network technology. I don't know how often current GSM networks must force GSM phones into AMR mode, but higher capacity would allow for the EFR codec to be used more often.

    Any more questions?
     
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  5. Bugwart

    Bugwart Bronze Senior Member
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    Location:
    Eastern Pennsylvania
    My Phone:
    Samsung SCH i760,
    Wireless Provider(s):
    SKT, Verizon, China Mobile, EPlus
    The following is somewhat unclear:

    GSM phones today are capable of both and which one your phone uses depends on how full the network is. It will be the same way with wCDMA.

    Today's GSM phones work <u>only</u> on GSM systems, except for those which are designed for GPRS or EDGE. A GPRS (or EDGE) phone will operate on legacy GSM systems. These phones are backwards compatible, but not forwards compatible. That means that a GPRS phone will work on a GSM syste, but not on an EDGE system.

    Today's commercially available WCDMA (or UMTS) handsets only work on WCDMA systems. The Japanese and Isle of Man WCDMA handsets are single mode and they will not hand-off to legacy TDMA systems such as GSM or GPRS. Future WCDMA handsets will be multi-mode to allow roaming on non-WCDMA systems.

    A fully backwards compatible WCDMA handset will need 4 individual modes of operation:
    1. Wide band CDMA
    2. EDGE - enhanced multi connection packet switched TDMA
    3. GPRS - multi connection packet switched TDMA
    4. GSM - circuit switched TDMA

    In addition, such handsets will need to be able to operate on at least 4 frequencies (900/1800/1900 MHz for GSM/GPRS/EDGE and &gt;2000 MHz for WCDMA) if they are to be capable of roaming worldwide.

    Such a quad band/quad mode phone will be complex.
     
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  6. Maximinfo

    Maximinfo New Member

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    My next questions. By the way thank you northform!

    Are both CDMA techniques DS/CDMA and FH/CDMA used in WCDMA? If they are, how are they used? I generally now how DS/CDMA technique works but what about FH/CDMA.. What advance we get from frequency hopping if all channels are in the same frequency. Can we talk about wideband anymore?

    If basestation has to receive all users from different distances with same power, how is transmitter power control realised in WCDMA? Is that only DS/CDMA problem? Are the phrases open loop and closed loop connected to this?

    You can use low transmitter power in WCDMA and that helps to keep energy consumption low and that is understandable. But how the handover in WCDMA reduses energy consumption? And how does the handover technique reduces noise and enlarges capasity?
     
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