Why TDM time slot time duration is 577us ??

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Nataraju A B natarajuab.tech at gmail.com
Sun Jan 9 17:30:58 UTC 2011


Thanks for the useful info, Is there some reference doc which deals in
details on this timings... ?

2011/1/8 Fadil Berisha <f.koliqi at gmail.com>

> Bit rate duration is determined from physical channel throughput for
> particular modulation schema. GMSK modulation is used with constant BT
> = 0.3, where  B is the 3dB bandwidth of the theoretical Gaussian
> filter and T is duration of input data bit. Knowing B, we calculate
> 1/T = 1625/6 ksymb/s  or approximately 270.833 ksymb/s. From here bit
> duration is 3.69.. μ s.
>
> Voice signal is processed in time intervals of 20ms = s/50. For that
> period of time throughput is [(1625/6) x (1000/50)] symbols. Because
> this number is fractional, let look at 6 times longer time interval.
> For time interval 120ms throughput is [1625 x 20] symbols or [13 x 125
> x 20] symbols or [26 x 1250] symbols or [26 x 8 x 156.25] symbols.
>
> From last result we can identify:
> Number of symbols in a burst = 156.25 symbols, and burst time 156.25 x
> 3.69... = 576,92μs
> Number of symbols in TDMA frame is 8 x 156.25 = 1250 symbols,
> Number of symbols in Multiframe is 26 x 1250 symbols.
>
>
>
>
>
>
>
>
> On Fri, Jan 7, 2011 at 8:51 AM, Nataraju A B <natarajuab.tech at gmail.com>
> wrote:
> >
> > Hi Andreas,
> > Thanks for the speedy reply.
> > The link which sent you is definitely useful. But the very basic question
> I wanted to get a clarification was that, what is the drive behind selection
> of burst time to be 577us.
> > For example the audio frequency can range upto 4Khz. The sampling
> frequency should be 8Khz. If each sample is of 8 bit accuracy. This lead to
> 64K bits of data. ......  If we explore further on these lines we should be
> able to correlate to the time 577us for each burst.
> > I wanted some more info these lines. What was/were the drives behind
> selection of this burst time. Otherwise what are the other end requirements
> led to selection of this burst time and in turn TDMA frame hierarchy.
> > Thanks,
> > Nataraju A B
> > On Fri, Jan 7, 2011 at 7:01 PM, Andreas.Eversberg <
> Andreas.Eversberg at versatel.de> wrote:
> >>
> >> in addition:
> >>
> >> Traffic Multiframe Structures - The 26 traffic multiframe structure is
> >> used to send information on the traffic channel. The 26 traffic
> >> multiframe structure is used to combine user data (traffic), slow
> >> control signaling (SACCH), and idle time period. The idle time period
> >> allows a mobile device to perform other necessary operations such as
> >> monitoring the radio signal strength level of a beacon channel from
> >> other cells. The time interval of a 26 frame traffic multiframe is 6
> >> blocks of speech coder data (120 msec).
> >> (http://www.althos.com/tutorial/GSM-tutorial-frame-structure.html)
> >>
> >> one encoded speech block lasts 20ms.
> >>
> >>
> >>        576,92307692307692307692307692308us per slot
> >>        4615,3846153846153846153846153846 per 8 slots (1 frame)
> >>        120ms per 26 frames (6 speech blocks)
> >>
> >>
> >>
> >
> >
> >
> > --
> > Thanks,
> > Nataraju A B
>



-- 
Thanks,
Nataraju A B
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