  We consider the weak target detection problem with unknown parameter in
colocated multiple-input multiple-output (MIMO) radar. To cope with the sheer
amount of data for large-size systems, a multi-bit quantizer is utilized in the
sampling process. As a low-complexity alternative to classic generalized
likelihood ratio test (GLRT) for quantized data, we propose the multi-bit
detector on Rao test with a closed-form test statistic, whose theoretical
asymptotic distribution is provided to generalize the actual detection
performance. Besides, we refine the design of quantizer by optimized
quantization thresholds, which are obtained resorting to the popular particle
swarm optimization algorithmthe (PSOA). The simulation is conducted to
demonstrate the performance variations of detectors based on unquantized and
quantized data. The numerical results corroborate our theoretical analyses and
show that the performance with 3-bit quantization approaches the case without
quantization.
