  This paper considers information-theoretic models for integrated sensing and
communication (ISAC) over multi-access channels (MAC) and device-to-device
(D2D) communication. The models are general and include as special cases
scenarios with and without perfect or imperfect state-information at the MAC
receiver as well as causal state-information at the D2D terminals. For both
setups, we propose collaborative sensing ISAC schemes where terminals not only
convey data to the other terminals but also state-information that they extract
from their previous observations. This state-information can be exploited at
the other terminals to improve their sensing performances. Indeed, as we show
through examples, our schemes improve over previous non-collaborative schemes
in terms of their achievable rate-distortion tradeoffs. For D2D we propose two
schemes, one where compression of state information is separated from channel
coding and one where it is integrated via a hybrid coding approach.
