  Consider a scenario of broadcasting a common content to a group of
cooperating mobile devices that are within proximity of each other. Devices in
this group may receive partial content from the source due to packet losses
over wireless broadcast links. We further consider that packet losses are
different for different devices. The remaining missing content at each device
can then be recovered, thanks to cooperation among the devices by exploiting
device-to-device (D2D) connections. In this context, the minimum amount of time
that can guarantee a complete acquisition of the common content at every device
is referred to as the "completion time". It has been shown that instantly
decodable network coding (IDNC) reduces the completion time as compared to no
network coding in this scenario. Yet, for applications such as video streaming,
not all packets have the same importance and not all devices are interested in
the same quality of content. This problem is even more interesting when
additional, but realistic constraints, such as strict deadline, bandwidth, or
limited energy are added in the problem formulation. We assert that direct
application of IDNC in such a scenario yields poor performance in terms of
content quality and completion time. In this paper, we propose a novel Content
and Loss-Aware IDNC scheme that improves content quality and network coding
opportunities jointly by taking into account importance of each packet towards
the desired quality of service (QoS) as well as the channel losses over D2D
links. Our proposed Content and Loss-Aware IDNC (i) maximizes the quality under
the completion time constraint, and (ii) minimizes the completion time under
the quality constraint. We demonstrate the benefits of Content and Loss-Aware
IDNC through simulations.
