# A Reliable Low-Latency Multipath Routing Algorithm for Urban Rail Transit Ad Hoc Networks
## 3 The Improved Multipath Routing Algorithm
### RLLMR Algorithm
Therefore, the LRM scheme can effectively reduce repair latency and improve transmission efficiency. #### 4.2.2 Packet Loss Rate Results

In this section, first, the effect of the traditional AODDV routing algorithm based on the minimum hop count is simulated and compared with the AMS routing scheme based on the link cost function on the packet loss rate. During the experiments, the path hop count and link quality are considered to have the same degree of contribution to delay and reliability. The simulation results are shown in Figure 11.

Figure 11: The relationship of packets loss rate with sent packets. Figure 10: Average end-to-end latency in a bad network environment. As shown in Figure 11, the packet loss rate using the AOMDV routing algorithm is higher than that of the AMS routing algorithm, which is because the path selection based on link cost enables the selection of paths with fewer hop counts and good network quality, reducing the impact of bad path quality on data transmission and improving the success rate of packet delivery. Second, considering that the route maintenance mechanism can improve the packet loss rate of data transmission, the packet loss rate of traditional AODV routing, traditional AOMDV routing, and AMS routing with the addition of an LRM scheme is simulated and compared, respectively, under different network quality environments. The simulation results are shown in the following figure. As shown in Figures 12 and 13, the traditional AODV route is more serious in the packet loss rate due to the lack of a routing maintenance scheme. Using the AOMDV alternate route maintenance mechanism, the lost packets can be retransmitted through multiple alternate paths, which reduces the packet loss rate to a large extent and reduces the effect of the network environment. While the AMS routing based on the LRM scheme has about the same packet loss rate as AOMDV routing when the network quality is good, its packet loss rate will be higher than that of AOMDV routing in a poor network quality environment, which is because the temporary path established by the maintenance node cannot improve the quality of the whole path. However, considering the high maintenance cost and long repair time of the AOMDV routing maintenance scheme, the LRM scheme can reduce the cost of the alternate paths and enable a reduction in the repair time. On the whole consideration, the AMS routing with the LRM scheme has a better performance. In addition, using a small number of alternate paths to ensure high-reliability requirement services and using the LRM scheme for the rest of the services can be considered in future studies. #### 4.2.3 Throughput Results

Throughput means the average rate at which data packets successfully reach the destination node from the source node. In this section, the throughput is simulated under different routing protocols based on the difference in network environment quality, and the simulation results are shown in Figures 14 and 15. As shown in the figure, the RLLMR algorithm based on AMS and LRM proposed in this paper has a higher throughput compared with traditional AOMDV. The reason is that the packet loss rate of AOMDV based on the alternate path is the lowest, but its repair time is longer, while the LRM-based multipath routing algorithm, although inferior to AOMDV in terms of the packet loss rate, reduces the route maintenance latency significantly. Therefore, the RLLMR algorithm can improve the throughput of the system. Figure 12: Packets loss rate in a good network environment. ## 5 Discussion

Through the simulation experiments conducted in Section 4, it can be found that the RLLMR algorithm proposed in this paper performs better in terms of latency, reliability, and throughput than AODV and AOMDV. Figure 14: Throughput in a good network environment. Figure 13: Packets loss rate in a bad network environment. Figure 6:0 Throughput in a bad network environment. First, during the route discovery process, AODV and AOMDV find the destination node through the multi hop transmission of REEQ.