Abstract:

The pure ALOHA channel access method defined in the standard LoRaWAN protocol can cause a lot of collisions and transmissions failed when in a heavy load, it challenges the scalability and reliability of the LoRa network greatly. A new channel access method, LBT-SA （Listen Before Talk combined with Simulated Annealing）, is proposed. This method reduces the probability that multiple devices access the channel by detecting the channel before sending, and searches for a smaller backoff time by taking the backoff time required for successful transmission as the initial value. Simulation results show that LBT-SA can not only maintain the packet delivery rate provided by LBT with binary exponential backoff algorithm, but also minimize the unnecessary backoff in the transmission, thus reducing the delay. In a scenario where up to 10,000 end-devices access a single gateway, the average backoff time of the algorithm is reduced by at least 16.38%.

Key words: LoRaWAN, channel access method, listen before talk, simulated annealing algorithm, competition window

摘要：

标准LoRaWAN协议中定义的纯ALOHA信道接入方法在网络负载较大时会造成大量碰撞，使LoRa网络的可扩展性和可靠性受到极大挑战。为此提出了一种将先听后说与模拟退火相结合（Listen Before Talk combined with Simulated Annealing，LBT-SA）的LoRa信道接入方法。该方法通过在设备发送之前先监听信道，降低信道被同时接入的概率，并以成功传输所需退避时间为初始值，搜索更小的退避时间。仿真结果表明，LBT-SA和基于二元指数退避算法的先听后说（Listen Before Talk，LBT）方法在包成功传输率方面保持了高度的一致，并且LBT-SA在周期传输过程中逐渐减少了不必要的退避时间，从而减少了时延。在多达10 000个终端接入单个网关的场景中，该算法的平均退避时间至少降低了16.38%。

关键词: LoRaWAN, 信道接入方法, 先听后说, 模拟退火算法, 竞争窗口