Research On Throughput Fairness And Scalability In LoRa Networks

With growing popularity,LoRa networks are pivotally enabling Long Range connectivity to low-cost and powerconstrained user equipments(UEs).Due to its wide coverage area,a critical issue is to effectively allocate wireless resources to support potentially massive UEs in the cell while resolving the prominent near-far fairness problem for cell-edge UEs,which is challenging to address due to the lack of tractable analytical model for the LoRa network and its practical requirement for low complexity and low-overhead design.To achieve massive connectivity with fairness,we investigate the problem of maximizing the minimum throughput of all UEs in the LoRa network,by jointly designing high-level policies of spreading factor(SF)allocation,power control,and duty cycle adjustment based only on average channel statistics and spatial UE distribution.By leveraging on the Poisson rain model along with tailored modifications to our considered LoRa network,we are able to account for channel fading,aggregate interference and accurate packet overlapping,and still obtain a tractable and yet accurate closed-form formula for the packet success probability and hence throughput.We further propose an iterative balancing(IB)method to allocate the SFs in the cell such that the overall max-min throughput can be achieved within the considered time period and cell area.In the same way,we extend the formula in single gateway to the multi gateway network.Under 1-Reuse scheme,we can get the max-min throughput of all UEs considering the interference from multiple gateways,and then we can get the relationship between the spatial throughput and the gateway density.Moreover,the effect of multi-gateway reception in LoRa is also investigated.Numerical results show that the proposed scheme with optimized design greatly alleviates the near-far fairness issue,and significantly improves the cell-edge throughput.In addition,the implementation of duty cycle in gateway downlink transmission is also important in LoRa network.If the downlink duty cycle is too high,it will violate the LoRaWAN standards and reduce the fairness and stability.Conversely,it will reduce the spectrum efficiency.In a large scale network,the uplink and downlink transmissions generate random and complex coupling due to co-channel interference,which makes it difficult to meet the specific requirement of downlink duty cycle.In order to solve this problem,we propose a method based on conditional transmission probability to achieve the specific duty cycle of LoRa downlink transmission,while at the same time,satisfying the different downlink priority requirements of the users.