Transmission - 3DTV: Processing and Transmission of 3D Video Signals - page 121

formats all have a multi-layered bit stream structure. This layered structure
may comprise parts that are perceptually more important than others or
the decoding of some parts of the multi-layered 3D video bit stream is only
possible if the corresponding more important parts are received correctly (e.g.
base view or base quality layer). The effective exploitation of such importance
and redundancy characteristics in 3D video representation formats and
their associated coding approaches can be used to improve the system's
performance in terms of spectral efficiency and capacity. At the physical layer
of OFDMA-based mobile broadband systems, such as WiMAX and LTE, the
radio transmission properties are described using a set of parameters, such
as the modulation type (e.g. QPSK, 16-QAM, 64-QAM), the FEC code type
(e.g. CTC, BTC), and the channel-coding rate (e.g. 1/2, 2/3, 3/4, 5/6), i.e.
the MCS. The base station can utilize different MCSs to achieve the best
trade-off between the spectrum efficiency and the resulting application level
throughput. As a result, different transmission techniques can be adopted for
the delivery of a multi-layered 3D video bit stream over a mobile broadband
network.
In the first technique, referred to here as the robust transmission technique,
the different components of the multi-layered 3D video bit stream are
transmitted using a robust modulation type and a low channel-coding rate,
such as QPSK 1/2. In this case, the service quality is ensured in an average
RF environment, such as the case in mobile broadcast systems, where the
transmission is typically designed to serve the worst-case user. However,
the utilization of this technique would exhaust the available radio resources
and hence would affect the number of offered mobile 3DTV channels and/or
other services (e.g. VoIP, data, etc.). The second technique, referred to here as
the radio resource efficient transmission technique, aims to offer a 3D video
service as efficiently as possible. The different components of the multi-
layered 3D video bit stream are transmitted using an efficient modulation
type and a high channel-coding rate, such as 64-QAM 3/4, if allowed by
the RF conditions of the target coverage area of the BS. However, in this
case, the area over which the 3D video service can be offered will be limited
and when entering difficult or bad reception conditions, the subscribers may
experience sudden service interruptions instead of soft degradation in 3D
video quality perception.
In the third technique, referred to here as the optimized transmission
technique, the first and the second transmission techniques are combined
into a unified technique so that the limitations of each are overcome by
the primary advantage of the other. In this case, the coverage area of the
BS can be divided into several overlapping transmission regions, where the
BS multicasts/broadcasts the different components of the multi-layered 3D
video bit stream in parallel using different spectrally-efficient MCSs. For
example, the baseline component, which can be a two-channel stereo video
encoded jointly using H.264/MVC is transmitted using a robust MCS (e.g.
QPSK 1/2). This allows the subscribers with 3D-capable devices to receive