Research On Iot MAC Protocols For LoRa

With the development of the Internet of Things,especially in the context of the emergence of applications like Smart Grids,Smart Transportation,Smart Agriculture and so on,establishing large scale low power wide area networks with high efficiency is critical.As the conventional communication techniques can't fulfill this requirement,one of the LPWAN technologies which is said to be promising for various applications,LoRa,is attracting more and more attention from the industry and the academy because of its long communication range and great resistance to interference.On the other hand,In the future,a great challenge that IoT needs to overcome is how to efficiently handle the continuously growing amount of traffic load and devices in the networks,as well as the variety of traffic types.In order to handle this challenge,the design of efficiency MAC protocols is critical.Because the MAC protocol that is now being used in LoRa networks,the ALOHA-based LoRaWAN protocol is not able to handle this challenge well,it's urgent to adapt more efficient MAC protocols to LoRa networks.Therefore,this thesis studies on mac protocols for LoRa networks at the case of a large number of nodes and under heavy traffic load.The main contributions of this work are summarized as follows: Firstly,this thesis models a LoRa network with the help of a link measurement model,a link performance model and an application model.A LoRa simulation module is proposed to implement these models based on a discrete event simulator NS3,and then this module is utilized for the simulations on the ALOHA-based LoRaWAN protocols.The simulation results show that the PDR(packet delivery rate)and throughput of LoRaWAN protocol is low at the case of a large number of nodes and under heavy traffic load.Secondly,to solve the transmission collision issue of LoRa networks with a large number of nodes and under heavy traffic load,a MAC protocol is proposed based on Distributed Queues.In the proposed protocol,a tree-splitting contention resolution is conducted through a contention window and a feedback window,therefore nodes are capable of transmitting data in a collision-free way.The simulation results show that the proposed protocol has better performance in terms of PDR and throughput compared with LoRaWAN.Lastly,for solving the low throughput issue of LoRa networks with a large number of nodes and under heavy traffic load,a MAC protocol is proposed for LoRa networks based on CSMA/CA,in which carrier sensing and random backoff are exploited to reduce the probability of collisions.Meanwhile an analytical model is set up for this protocol through Discrete Markov Chain,and then its throughput is derived.The simulation results show that the proposed protocol has better performance than LoRaWAN in terms of PDR and throughput,and also has higher throughput than the proposed DQ-based protocol while having a good PDR performance.