# Intersection-Based Link-Adaptive Beaconless Forwarding in Urban Vehicular Ad-Hoc Networks
## 4 Performance Analysis
### Simulation Results
#### 4.3.1 Source Transmission Rate Variation
For most of the source transmission rate variation cases (100 kbps \(\leq R_{src}\leq\) 400 kbps), both ILBFC and LBF yield better performance when compared to DBD and BLR. This is due to their better winner relay management based on the link duration, thereby minimizing the delay caused by the relay selection process. Specifically, for the source transmission rate variation cases (100 kbps \(\leq R_{src}\leq\) 400 kbps), the mean values of the average ETE delay of ILBFC, LBF, DBD, and BLR are 17.3 ms, 17.1 ms, 20.5 ms and 20.4 ms, respectively. At higher source transmission rate (\(R_{src}=\) 500 kbps), the low average ETE delay of DBD and BLR is simply because of their degraded PDR performance highlighted in Figure 5, as an increase in \(R_{src}\) results in more data packets being dropped due to buffer overflow. As far as LBF and ILBFC are concerned, LBF at \(R_{src}=\) 500 kbps results in relatively high average ETE delay when compared to ILBFC, which is due to multiple relay nodes forwarding the same data packet at single hop level leading to redundant data packets flowing throughout the network and causing packet collision and network congestion. This happens because of the relay nodes moving out of the  
Figure 5: Performance comparison of ILBFC with LBF, DBD and BLR versus source transmission rate while keeping the maximum speed of the node equals 50 km/hr and the number of nodes equals 40. (a) PDR versus source transmission rate; (b) Average ETE delay versus source transmission rate; (c) PRC versus source transmission rate. forwarding zone while still being in the \"winner\" state. Also, these relay nodes may further travel in a direction where there are either none or very few suitable relay node contenders to further forward the packet, thereby resulting in longer routes to destination causing high average ETE delay. ILBFC, on the other hand, performs better than LBF while also offering better PDR performance due to its accurate \(\delta_{eff}\) estimation which is based on the location information of road intersections. This results in less longer routes to destination. Also, at single hop level, the chances of more than one relay node being selected to forward the data packet is reduced, hence yielding lower average ETE delay. Figure 5c shows the PRC performance of protocols accentuating their efficiency in terms of forwarding the data packet in unicast way with respect to varying source transmission rate. With an average PRC value of 8.9, DBD results in the highest PRC indicating low unicast efficiency. The major reason for this is its lack of forwarding zone criteria, which leads to multiple relay nodes being formed at single hop level. The decrease in PRC for DBD with increasing \(R_{src}\) is simply because of the increase in the number of packets being dropped by the intermediate relay nodes due to packet collision. In contrast, with an average PRC value of 1.5, BLR yields the lowest PRC, implying high unicast efficiency. One of the main reasons is that unlike others, BLR performs relay selection for every data packet received, thereby minimizing the multiple relay nodes at single hop level. Another reason is the high packet drops encountered at intermediate relay nodes due to buffer overflow. This further results in less data packets being forwarded and hence contributes towards low PRC. The impact of using the road intersection information in correctly estimating link duration on PRC performance can be clearly seen when comparing LBF and ILBFC. Due to its accurate \(\delta_{eff}\) estimation, the ILBFC protocol which has an average PRC value of 5.4, ensures relatively less multiple relay node formation at single hop level when compared to LBF which has an average PRC value of 7.7, thereby resulting in lower PRC.