  An integrated sensing and backscatter communication (ISABC) system is
introduced herein. This system features a full-duplex (FD) base station (BS)
that seamlessly merges sensing with backscatter communication and supports
multiple users. Multiple access (MA) for the user is provided by employing
rate-splitting multiple access (RSMA). RSMA, unlike other classical orthogonal
and non-orthogonal MA schemes, splits messages into common and private streams.
With RSMA, the set of common rate forms can be optimized to reduce
interference. Optimized formulas are thus derived for communication rates for
users, tags, and the BS's sensing rate, with the primary goal of enhancing the
transmission efficiency of the BS. The optimization task involves minimizing
the BS's overall transmission power by jointly optimizing the BS's beamforming
vectors, the tag reflection coefficients, and user common rates. The
alternating optimization method is employed to address this challenge. Concrete
solutions are provided for the received beamformers, and semi-definite
relaxation and slack-optimization techniques are adopted for transmit
beamformers and reflection coefficients, respectively. For example, the
proposed RSMA-assisted ISABC system achieves a 350% communication rate boost
over a nonorthogonal multiple access-assisted ISABC, with only a 24% increase
in transmit power, leveraging ten transmit/reception antennas at the BS.
