  The dual-functional radar-communication (DFRC) system is an attractive
technique, since it can support both wireless communications and radar by a
unified hardware platform with real-time cooperation. Considering the appealing
feature of multiple beams, this paper proposes a precoding scheme that
simultaneously support multiuser transmission and target detection, with an
integrated continuous phase modulation (CPM) and linear frequency modulation
(LFM) signal, based on the designed dual mode framework. Similarly to the
conception of communication rate, this paper defines radar rate to unify the
DFRC system. Then, the maximum sum-rate that includes both the communication
and radar rates is set to be the objective function. Regarding as the optimal
issue is non-convex, the optimal problem is divided into two sub-issues, one is
the user selection issue, and the other is the joint beamforming design and
power allocation issue. A successive maximum iteration (SMI) algorithm is
presented for the former issue, which can balance the performances between the
sum-rate and complexity; and maximum minimization Lagrange multiplier (MMLM)
iteration algorithm is utilized to solve the latter optimal issue. Moreover, we
deduce the spectrum characteristic, bit error rate (BER) and ambiguity function
(AF) for the proposed system. Simulation results show that our proposed system
can provide appreciated sum-rate than the classical schemes, validating the
efficiency of the proposed system.
