Design of Antennas for Handheld DVB-H ... - Lunds tekniska högskola

2.1.5.2 Time slicing
A large problem with handheld terminals is the limited battery capacity. It is
impossible to receive and decode a broad band, high data-rate stream like the
DVB-T data stream with a battery terminal. The receiver and demodulation part in
the terminal would use too much power and the battery would run out quickly. In
the beginning of the development of DVB-H it was shown that the power
consumption of a DVB-T receiver is about 1 Watt, which is too much [14]. A
some-what lower value seems possible but the desired target of 100 mW as a
maximum threshold for the entire front end incorporated in a DVB-H terminal is
still unobtainable for a DVB-T receiver.
A considerable drawback for battery-operated terminals is the fact that with DVB-
T, the whole data stream has to be decoded before any one of the services (TV
programs) of the multiplex can be accessed. The main reason why DVB-H
consumes less power is that the receiver only has to receive and process the parts
of the data stream that contains the information needed for the selected service.
For this to be possible the data stream needs to be reorganized in a suitable way.
With DVB-H, service multiplexing is performed in a pure time-division
multiplex. The data of one particular service are therefore not transmitted
continuously but in compact periodical bursts with interruptions in between. In the
interruption between bursts, other services are sent. This leads to a continuous
data stream. This data stream can be received in time intervals where the receiver
is synchronized with the service you want to receive. Then the receiver can be
shut down when the other services that you have no interest in are sent. This way
of dividing the signal is called time slicing [15].
When time slicing is used to receive the signal it saves a lot of power because the
receiver can be turned off most of the time. When the receiver is on, the received
signal is buffered in a memory and then read out from the buffer in the service
data-rate. When the receiver is turned on the next time and receives a new data
stream, this data is buffered in the memory and the video can be played
continuously. For the receiver to know when it is time to turn itself on again after
an off-time, data containing information about how long the receiver should be
turned off between the bursts, has to be sent in each burst.
The duration of one burst is in the range of several hundred milliseconds whereas
the power save time may amount to several seconds. The receiver has to be turned
on before it is time to receive data and therefore it is turned on 50-250 ms before
calculated receiving time. Depending on the ratio between on time and off time,
the resulting power saving may be more than 90 %.
As an example, figure 2.4 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
11