Outage of Multiple Access Channels With Applications to Performance Analysis of Massive MTC Transmissions

In this letter, we study a slotted grant-free access scheme for massive machine-type communications (mMTC) in narrowband Internet of Things (IoT) environments. We allow multiple IoT devices to transmit simultaneously at the beginning of each time slot over the multiple access channel (MAC), and the AP jointly detect the transmissions. The outage of the MAC is defined by an event that transmission rates are outside the instantaneous capacity region. Considering all the individual transmission rate constraints and the total sum transmission rate constraint, we obtain a lower bound of the outage probability of the MAC with distinct average channel quality and distinct transmission rates among devices. Then we derive the throughput of the overall system and the transmission-success probability of an individual device. We show that our analyses are very accurate and that all the performance highly depends on the turn-on probability of each device to transmit over the MAC.