TAMK University of Applied
Sciences
Escola Politécnica Superior de Castelldefels
Marcos Tejedor Alonso
32 (44)
4.1.1 Time-Slicing
Mobile devices have a limited battery capacity and they cannot accommodate TC chips inside that consumes
too much energy. DVB-H specifies that consumptions over 100 mW are impossible in
hand-held terminals,
and the commercial chips consume between 200mW to 500mW or higher depends
on the TV chip that is
used and the purpose of it. The terminal, because of the demodulating and decoding of high data-rate, also
involves a power dissipation in the tuner and the demodulator part. For this reason
is used the technique
called time slicing.
The time slicing is a power-saving algorithm based on the transmission of different services based on time-
multiplexed. In such a way, the data is not transmitted continuously but in periodical bursts with interruptions
between these ones. The signal can be received selected by time. The terminal synchronizes with the bursts
of the services that the user wants, and it turns to a power save mode during the time that another services
are being transmitted. This is a direct measure to save power in the batteries of the hand held receivers. The
bursts that enter in the receiver have to be buffered and read at the service data-rate. Time slicing requires a
sufficiently high number of multiplexed services and a certain minimum burst.
The amount of data that
contains each bursts has to be sufficient to do the power-save period. Depending on the ratio of on-time /
power-save time, the resulting power saving may be more than 90 %.
The figure 10 shows a cut-out of a data stream containing time-sliced services. One quarter of the assumed
total capacity of the DVB-T channel of 13.27 Mbit/s is assigned to DVB-H services
whereas the remaining
capacity is shared between ordinary DVB-T services. This example shows that it is feasible to transmit both
DVB-T and DVB-H within the same network. [9]
Fig.10: Cut-out of data stream
Time slicing introduces another benefit for hand-hand terminals. The power-save
periods may be used to
search channels with the service, selected by the user, in neighbouring radio cells. In this way, the terminal
can works at the border between two cells ad can offer the service which remains imperceptible for the user.
So, this technique allows a soft handover when the mobile phone is moving from one cell to another one.
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