# Collision Avoidance Resource Allocation for LoRaWAN
###### Abstract  
The number of connected IoT devices is significantly increasing and it is expected to reach more than two dozens of billions of IoT connections in the coming years. Low Power Wide Area Networks (LPWAN) have become very relevant for this new paradigm due to features such as large coverage and low power consumption. One of the most appealing technologies among these networks is LoRaWAN. Although it may be considered as one of the most mature LPWAN platforms, there are still open gaps such as its capacity limitations. For this reason, this work proposes a collision avoidance resource allocation algorithm named the Collision Avoidance Resource Allocation (CARA) algorithm with the objective of significantly increase system capacity. CARA leverages the multichannel structure and the orthogonality of spreading factors in LoRaWAN networks to avoid collisions among devices. Simulation results show that, assuming ideal radio link conditions, our proposal outperforms in 95.2% the capacity of a standard LoRaWAN network and increases the capacity by almost 40% assuming a realistic propagation model. In addition, it has been verified that CARA devices can coexist with LoRaWAN traditional devices, thus allowing the simultaneous transmissions of both types of devices. Moreover, a proof-of-concept has been implemented using commercial equipment in order to check the feasibility and the correct operation of our solution.  
LoRa MAC; LoRaWAN; capacity; PER; throughput; path loss Article Collision Avoidance Resource Allocation for LoRaWAN [PERSON], N., N., J.  
end-device in a sub-band and, also, by the number of collisions produced by the use of low data rates (DRs). So, the main challenge that we have addressed is the coordination of the resources over the ALOHA channels in order to achieve the maximum possible capacity. For this reason, this paper proposes CARA (Collision Avoidance Resource Allocation for LoRaWAN networks), a modification of the LoRaWAN MAC layer which improves network capacity by employing a smart algorithm for resource assignment.  
CARA is designed to cover any kind of scenario, both rural and urban and even indoor scenarios. Specifically, as CARA exploits the LoRaWAN ALOHA channel access, it is designed for applications such as smart metering, smart agriculture, smart cities, smart homes, smart healthcare, and so forth. Based on the results obtained in the simulations, it outperforms the standard LoRaWAN channel access in urban environments of up to \(8\times 8\) km\({}^{2}\).  
The paper is structured as follows. Section 2 deals with the related work. Section 3 describes the main technical aspects about LoRa and LoRaWAN. Section 4 presents the novel LoRaWAN MAC design proposed in this paper. Section 5 details all the experimentation part and evaluates the performance of our solution by means of simulations.The coexistence in a homogeneous network with CARA and LoRaWAN traditional devices has been checked and verified in Section 6. Our solution has been implemented using commercial hardware in order to provide a proof-of-concept, which is explained in Section 7. Finally, Section 8 draws the main conclusions of this work.