Collision-free optimal packet scheduling algorithm for multi-hop wireless IoT networks

One of the key challenges for the IoT (Internet of Things) evolution is the network connectivity provision to a large number of resource-limited low-cost IoT devices. To meet this challenge, various efforts have been made in today's wireless network technologies, such as LTE eMTC, 5G NB-IoT, IEEE 802.11ah, BLE, etc. Meanwhile, most of these technologies consider multi-hop wireless relaying to extend the wireless coverage and to enhance the network transmission capacity. Despite the benefits, however, the usage of multi-hop relaying has been limited in the real world, because of the performance degradation caused by the self-interference between adjacent wireless links. In this paper, we tackle the problem of alleviating the performance degradation in the multi-hop wireless network for IoT devices. In particular, we target low cost IoT devices that are equipped with inexpensive wireless links such as WiFi, IEEE 802.15.4, and Bluetooth. Our approach is to avoid self-interference by controlling the transmission timing at each hop. More specifically, our design goal is to minimize the data delivery delay for fast IoT sensing by preventing packet collisions (i.e., collision-free transmission). Since the retransmission at the IoT devices is eliminated, buffering at the intermediate nodes is not necessary so that no extra storage is consumed at the IoT devices to store the data being relayed. We present an algorithm to produce the packet transmission schedule at each hop. We prove that our algorithm is optimal in terms of data delivery delay (i.e., minimal delay is guaranteed) while collision between transmissions is completely avoided.