# Intersection-Based Link-Adaptive Beaconless Forwarding in Urban Vehicular Ad-Hoc Networks
## 4 Performance Analysis
### Simulation Results
#### 4.3.1 Source Transmission Rate Variation  
This section shows the impact of source transmission rate on the performance of the protocols in terms of PDR, average ETE delay and PRC. The transmission rate of a source node (\(R_{src}\)) is defined as follows:  
\[R_{src}=S_{bits}/T_{intarr}, \tag{26}\]  
where \(S_{bits}\) is the data packet size in bits and \(T_{intarr}\) is the inter-arrival time of the data packets. Figure 5 highlights the impact of source transmission rate variation on the performance of different routing protocols. Specifically, \(R_{src}\) is varied from 100 kbps to 500 kbps with an incremental step of 100 kbps. Also, for this scenario, the maximum speed of the node is set to 50 km/hr, and the number of nodes (one static destination and the rest are mobile nodes) is fixed to 40. Figure 5a shows the PDR performance of the protocols with respect to varying \(R_{src}\). BLR protocol at \(R_{src}\) equals 100 kbps yields the lowest PDR of all. This is because every received data packet that satisfies the forwarding zone condition has to wait a certain duration depending upon the waiting time criteria before it can further forward the packet. This results in a large number of data packets being queued in buffer and may further lead to data packet being dropped once the buffer is full. Therefore, with increasing \(R_{src}\) more data packets are dropped, thus resulting in decreased PDR. The DBD protocol, on the other hand, although it performs better than BLR protocol at \(R_{src}\) equals 100 kbps, its performance drops drastically with increasing \(R_{src}\). The major reason for this is due to its stringent winner relay management conditions. Unlike highways, where the relative velocity among the vehicles is quite stable, in an urban environment there exist high relative velocity fluctuations among vehicles. Hence, it will be difficult for relay nodes to satisfy the winner relay management condition (\(0.75\times r\leq d\leq r\)). Therefore, for most of the received data packets, the operation of DBD will be similar to BLR but without forwarding zone, which will further increase packet collision, thereby degrading the PDR performance. Also, ignoring the nodes moving in opposite direction for contention process may reduce the number of suitable contenders for forwarding the data packets. ILBFC and LBF show relatively high PDR performance due to their winner relay management condition which is based on the link duration among vehicles, thereby more data packets are forwarded in \"winner\" state resulting in fewer data packets being dropped due to buffer overflow. However, LBF at high source transmission rate (\(R_{src}\) equals 500 kbps) performs worse than ILBFC because of its lack of road adaptive features. Inaccurate \(\delta_{link}\) can lead to relay node staying in \"winner\" state for too long. This increases the chances of relay node moving out of the forwarding zone, thereby resulting in multiple relay nodes forwarding redundant data packet throughout the network, hence leading to higher chances of packet collision. Also, another drawback of relay node in the \"winner\" state moving out of the forwarding zone is the fact that it may travel in a direction where there are either none or very few suitable contending nodes available to further forward the data packet towards destination. In contrast, ILBFC limits \(\delta_{link}\) based on the next nearest intersection to more accurate \(\delta_{eff}\) while also checking the relative position of relay node in the \"winner\" state with respect to previous sender. This ensures that \"winner\" relay node does not move in the wrong direction, while also reducing the chances of the \"winner\" relay node moving out of the forwarding zone, hence resulting in superior  
PDR performance when compared to rest. For this scenario, the average PDR performance gains of ILBFC over LBF, DBD and BLR are 0.2%, 13.2% and 10.5%, respectively. Figure 5 depicts the average ETE delay of the data packets received at the destination.