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GMSK , 8PSK

Viewing 13 posts - 1 through 13 (of 13 total)
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  • #53900 Reply
    Ran
    Guest

    Ive read that usin 8psk we can transmit 3 bits per symbol then y dont we use it for GSM and gprs y we use gmsk only.

    #53901 Reply
    pix
    Guest

    Ran,

    GMSK allows stronger signals (a TRX emits stronger in GMSK than in 8PSK), so it’s better for coverage.

    GSM needs only about 12.2kb/s. 8PSK is not needed.

    However 8PSK might be applied to voice, in order to give better voice quality. Maybe in few years.

    #53902 Reply
    Ran
    Guest

    Hey pix thanx

    #53903 Reply
    R
    Guest

    hi pix

    since in 8psk , 3 bits are transmitted per symbol……. can i say that in this case the power required to transmit the same will be more?

    one more question:

    according to 8psk the data rate per tsl is 59.2kbps…… but my time slot can carry a max of only 16kbps…… how do i justify the concept ?/

    rgrds

    #53904 Reply
    Dangerous Minds
    Guest

    Hello R,

    The most straightforward explanation seems to be the that the higher EDGE coding schemes are not being used. I believe MCS-3 has a date rate of 16 kbps.

    In my network’s case, we had not purchased GPRS CS-3 and CS-4 coding schemes so our max GPRS throughput was always 12 kbps (CS-2 throughput)

    #53905 Reply
    R
    Guest

    hi danger mind

    in my n/w the samples of coding schemes for MCS 9 are the highest.
    The maximum throughput/tbf DL EDGE goes around 122kbps.
    The maximum throughput/tbf UL EDGE is 25/kbps.

    #53906 Reply
    pix
    Guest

    hello R,

    I’m surprised you don’t know the theory behind 8PSK 🙂 Actually each symbol = 3 bits.
    But what is one symbol ? In GMSK, one symbol is simply a certain phase.

    In 8PSK, a symbol is a certain phase + a certain amplitude (high amplitude or low amplitude).

    Because of that, when you measure the signal, you’ll actually measure an average of high and low amplitudes. Therefore the rxlevel is lower.
    FYI, the GMSK emmits always in “high” amplitude.

    Your second question is about the “physical” capacity of a radio timeslot ?

    One timeslot lasts 0.577 ms. During this amount of time, it’s possible to pack “x” symbols.

    In GMSK, x symbols = x bits
    In 8PSK, x symbols = 3*x bits.

    Therefore the bitrate is increased by 3.

    That’s approximation…
    Don’t forget that a timeslot rate in GMSK is 22 kb/s, containing useful + protection + signalling

    16kb/s is the timeslot rate on an E1 interface (Abis or Ater, for instance), which contains only the useful signal + some signalling.

    If your quesiton is about E1 timleslots, then… it’s simple : each radio timeslot in 8PSK will be carried by “n” terrestrial timeslots.
    For instance, 1 RTS in MCS9 will be carried by 4.5 TTS.

    Regards
    Pix

    #53907 Reply
    Henry
    Guest

    Hi Guys
    Please I need to know the Reason of Flactuating of RX Lev at DL/UL cases(RX Lev is OK when I start and then be decrease step by step)when EDGE is upgraded in a Network,

    Regards
    Henry

    #53908 Reply
    Henry
    Guest

    Sorry
    I mean at Download and Upload when I using EDGE,

    Regards
    Henry

    #53909 Reply
    pix
    Guest

    helo henry,

    i’m sorry, i don’t understand your question. could you illustrate it with an example ?

    #53910 Reply
    Henry
    Guest

    Hi Pix
    many thanks for your responce,
    the problem is when I connect my MS to GPRS or EDGE (in diffrent MCSs) in download or Upload cases, the RX-Lev is -64 (for Exp.)then the degredation will start, after secound will be -80 then to -90, -97, -103 then will comeback to -70 and then to -85, -95, -100, …etc,
    your feedback will be appreciate

    Regards
    Sardasht

    #53911 Reply
    pix
    Guest

    this is not a normal behaviour at all ! is there downlink power control in gprs ? I don’t think it’s 3GPP standard…

    so i’d say you have either a MS failure or a TRX failure. what brand of TRX are you using ? what brand of MS ?

    #53912 Reply
    Henry
    Guest

    Hi pix,
    as i checked there is no H/W problem in the Cell and is not one cell by the way,
    and the mobile that I use is Sony Erricson,
    regards
    Henry

Viewing 13 posts - 1 through 13 (of 13 total)
Reply To: Reply #53901 in GMSK , 8PSK
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