Combinatorial code designs for ultra-reliable IoT random access

We consider Combinatorial Code Designs (CCD) for ensuring ultra-reliability in the random access channel. By constructing user-specific repetition patterns to be utilised over a synchronised uplink frame consisting of a number of access slots, we guarantee successive reception up to a given number of simultaneously active users. Employing advanced receivers capable of Successive Interference Cancellation (SIC) further improves reliability. As an example, we consider a system with access frames of 24 bundled slots, repetition factor 3, and reliability target 99.999%. When compared to slotted repetition ALOHA, SIC provides a 30% gain in the tolerated user activity; CCD a 30% gain; whereas CCD combined with SIC provides a gain of more than 700%. These gains come at the cost of a strict limit on the supported user population. In the given example, the system can support a total of 2024 users.