LoRa MAC Protocol Design For Massive IoT Connectivity

With the rapid development of the Internet of Things(IoT),the vision of the communication between things-to-things and human-to-things has become possible.Long Range(LoRa)as one of the most promising Low Power Wide Area Networks(LPWAN)technologies,can provide a low-power,low-data-rate,and wide-area connection for the IoT end-devices.In most IoT scenarios,the traffic pattern of the end-devices is sporadic and the traffic size is generally small.Therefore,the user activity is sparse.LoRa WAN is the most popular upper layer protocol for LoRa and it utilizes an ALOHA-based Medium Access Control(MAC)protocol.Thus,it may arise serious collisions under the massive IoT connectivity,which results in a severe throughput degradation.To solve the massive connectivity problem,a novel MAC protocol is proposed through exploiting the LoRa capture effect.The key contributions of the thesis are three-fold described as follows:Firstly,a new receiver structure using oversampling is proposed,in order to tackle the problem that an Fast Fourier Transformation(FFT)module of the traditional receiver can only demodulate a single SF-specific signal.So three different odd/even SF signals can be simultaneously decoded in a single FFT module.The new receiver structure can efficiently handle the concurrent LoRa transmissions.A novel MAC protocol referred to Capture Effect-MAC(CE-MAC)protocol is then developed.CE-MAC protocol enables three different odd/even SF signals to be transmitted concurrently.Consequently,the capture effect can be better leveraged to resolve collisions.Compared to LoRa WAN,CE-MAC has a better throughput in the massive LoRa connectivity scenarios.Secondly,the theoretical derivation of the packet collision ratio is made for the CE-MAC protocol.The probability of the collisions before the capture effect works is analyzed,as well as the successful capture probability of the collided packets.Simulations show the reliability of the theoretical derivation.At last,the CE-MAC protocol is generalized into a multi-frequency situation.In the multifrequency CE-MAC protocol,the end-device failed to access owing to collisions can select the next transmission frequency based on a pseudo-random frequency sequence.Simulations verify that the multi-frequency CE-MAC protocol can further reduce the collision ratio and enhance the network throughput.