Semi-Grant-Free Orthogonal Multiple Access With Partial-Information for Short Packet Transmissions

Traditional multiple access schemes, as well as more recent preamble-based schemes, cannot achieve the extremely low latency, complexity, and collision probability required by the next-generation Internet-of-Things (IoT) networks to operate. To address such issues and further reduce the latency and packet loss, we introduce a novel semi-grant-free multiple access protocol for short packet transmission, the partial-information multiple access (PIMA) scheme. PIMA transmissions are organized in frames, and in the partial information acquisition (PIA) sub-frame of each frame, the base station (BS) estimates the number of active devices, i.e., the devices having packets waiting for transmission in their queue. Based on this estimate, the BS chooses both the total number of slots to be allocated in the data transmission (DT) sub-frame and the respective user-to-slot assignment. Although collisions may still occur due to multiple users assigned to the same slot, they are drastically reduced with respect to slotted ALOHA-based schemes, while achieving lower latency than both time-division multiple-access (TDMA) and preamble-based protocols, due to the extremely reduced overhead of the PIA sub-frame. We assess the performance of PIMA under various activation statistics, proving the robustness of the proposed solution to the traffic intensity, also with traffic bursts.