  Frequency-modulated continuous wave (FMCW) radar with inter-chirp coding
produces high side-lobes in the Doppler and range dimensions of the radar's
ambiguity function. The high side-lobes may cause miss-detection due to masking
between targets that are at similar range and have large received power
difference, as is often the case in automotive scenarios. In this paper, we
develop a novel code optimization method that attenuates the side-lobes of the
radar's ambiguity function. In particular, we introduce a framework for
designing radar transmit sequences by shaping the radar Ambiguity Function (AF)
to a desired structure. The proposed approach suppresses the average amplitude
of the AF of the transmitted signal in regions of interest by efficiently
tackling a longstanding optimization problem. The optimization criterion is
quartic in nature with respect to the radar transmit code. A cyclic iterative
algorithm is introduced that recasts the quartic problem as a unimodular
quadratic problem (UQP) which can be tackled using power-method-like iterations
(PMLI). Our numerical results demonstrate the effectiveness of the proposed
algorithm in designing sequences with desired AF which is of great interest to
the future generations of automotive radar sensors.
