requests from IoT devices want to be accepted.

Fig. \[fig:fig\_frame\_minislot\_structure\] depicts a frame and minislot structure for mIoT transmission in each mIoT slice[^2]. In this structure, both the frequency division multiplexing scheme and code division multiplexing scheme are leveraged to admit more IoT devices in the way of alleviating the mutual device interference. Particularly, the frequency division multiplexing scheme alleviates signal interference through orthogonal frequency allocation, and the code division multiplexing scheme mitigates the co-channel signal interference via reducing the cross-correlation of simultaneous transmissions. The combination of the two schemes may significantly mitigate interference experienced at an RRH. In this way, the QoS requirements of more IoT devices may be satisfied, and the RAN slicing system may support more IoT devices. For a mIoT slice $s \in \mathcal{S}^I$, each subframe includes $F_s$ orthogonal uplink physical RA channels (PRACHs). A single tone mode with a tone spacing of size of $a$ MHz is adopted for each uplink PRACH, which indicates that each PRACH occupies a PRB. At the beginning of each minislot, an active IoT device, i.e., the device’s queue is non-empty, will randomly choose a preamble from a set of non-dedicated RA preambles of size $\xi$ and transmit the preamble 