  The increasing demand for video streaming services is the key driver of
modern wireless and mobile communications. For robust and high-quality delivery
of video content over wireless and mobile networks, the main challenge is
sending image and video signals to single and multiple users over unstable and
diverse channel environments. To this end, many studies have designed
digital-based video delivery schemes, which mainly consist of a sequence of
digital-based coding and transmission schemes. Although digital-based schemes
perform well when the channel characteristics are known in advance, significant
quality degradation, known as cliff and leveling effects, often occurs owing to
the fluctuating channel characteristics. To prevent cliff and leveling effects
irrespective of the channel characteristics of each user, a new paradigm for
wireless and mobile video streaming has been proposed. Soft delivery schemes
skip the digital operations of quantization and entropy and channel coding
while directly mapping the power-assigned frequency--domain coefficients onto
the transmission symbols. This modification is based on the fact that the pixel
distortion due to communication noise is proportional to the magnitude of the
noise, resulting in graceful quality improvement, wherein quality is improved
gradually, according to the wireless channel quality without any cliff and
leveling effects. Herein, we present a comprehensive summary of soft delivery
schemes.
