## 4 Implementation
### GPSR_DA Algorithm
#### 4.1.2 Angle Calculation
Since control information has lower bandwidth requirements and needs to cover the entire moving area, the emphasis is on communication distance rather than bandwidth. Node movement speed is set to normal vehicle speed. The channels include a control channel based on the TDMA protocol and a data channel based on the CSMA protocol. Specific parameter settings are provided in \[\rho=L_{(N_{k}^{\prime\prime\prime},S)}=d_{(N_{k}^{\prime\prime\prime},SD)}sin\theta. \tag{2}\]8

### Evaluation Metrics

This paper compares and analyzes the proposed SD-GPSR routing method against traditional centralized SD-MANET routing methods, as well as distributed GPSR and AODV routing protocols, to verify the feasibility and effectiveness of the SD-GPSR approach. This paper collects the following performance metrics to analyze and evaluate the feasibility and effectiveness of the SD-GPSR routing method, as follows:

* **Total Control Overhead:** The total number of control packets transmitted in the network during the simulation time. * **Control Plane Overhead:** The total number of control packets exchanged between the network control plane and the data plane during the simulation time. * **Packet Loss Rate:** The ratio of lost data packets to the total number of data packets transmitted in the network, reflecting the reliability of network transmission. * **Average End-to-End Delay:** The average time required for data packets to travel from source nodes to destination nodes, which is a key metric for measuring the real-time delivery of traffic flows. ### Performance Analysis

#### 5.3.1 Impact on Service Flows

The simulation duration for this experiment is 600 s. The simulation results, as shown in Figure 5, reflect the average performance trends of various metrics for the four routing methods with varying traffic loads. In Figure 5a, the control overhead for all four routing methods increases with the increase in traffic load. AODV exhibits exponential growth in control overhead due to its broadcast-based route establishment, which becomes more pronounced with higher traffic loads. GPSR also shows exponential growth in control overhead, mainly because of the increased frequency of broadcasting location probe packets in the network. SD-GPSR and SD-MANET exhibit relatively smoother increases in control overhead. In Figure 5b, as the traffic load increases from 15 Kbps to 25 Kbps, the control plane overhead for SD-GPSR remains relatively stable, while SD-MANET experiences a significant increase in control overhead. This is primarily due to the increased number of control messages for topology maintenance and route request messages in the routing process caused by higher traffic loads. In Figure 5c, the packet loss rate trends for the three routing methods with varying traffic loads are shown. The packet loss rate of GPSR is higher than that of SD-GPSR and AODV when the traffic load is 5 Kbps, and there is little change in the packet loss rate as the traffic load increases from 5 Kbps to 10 Kbps. The packet loss rate is mainly influenced by changes in the position information of destination nodes and the presence of routing holes. As the traffic load gradually increases, congestion in nodes also contributes to packet loss, resulting in an increase in the packet loss rate. The packet loss rates of SD-GPSR and AODV gradually increase with the growth of the traffic load. During the transition from 0 Kbps to 15 Kbps, SD-GPSR shows a relatively moderate increase, but after reaching 15 Kbps, the packet loss rate increases significantly. This is because the increased traffic load may cause