  Initial timing acquisition in narrow-band IoT (NB-IoT) devices is done by
detecting a periodically transmitted known sequence. The detection has to be
done at lowest possible latency, because the RF-transceiver, which dominates
downlink power consumption of an NB-IoT modem, has to be turned on throughout
this time. Auto-correlation detectors show low computational complexity from a
signal processing point of view at the price of a higher detection latency. In
contrast a maximum likelihood cross-correlation detector achieves low latency
at a higher complexity as shown in this paper. We present a hardware
implementation of the maximum likelihood cross-correlation detection. The
detector achieves an average detection latency which is a factor of two below
that of an auto-correlation method and is able to reduce the required energy
per timing acquisition by up to 34%.
