# KQI Performance Evaluation of 3 GPP LBT Priorities for Indoor Unlicensed Coexistence Scenarios
## 5 Performance Assessment
### User Traffic  
Subsequently, Figures 6 and 7 display the results obtained at the level of KQI indicators for the user of FTP and RTVS services. They are shown in boxplot form taking into account the results of all the iterations and all frames in video streaming (which is why more samples have been captured). The first aspect that can be observed is that the behavior of the priorities is very similar to the one followed by the Background traffic, that is Priorities 1 and 2 present a longer delay (Figures 5(b) and 7(a)) and jitter values (Figure 6(b)) and lower throughput (Figure 5(a)) and PSNR (Figure 6(d)) than Priorities 3 and 4.  
Figure 5: Background traffic results.  
To deepen in these results, in Figure 8, a boxplot of the UPIs for both technologies is presented, measured in terms of the IP packages with prefixed MAC to channel delays so that only the delay introduced by the access to the channel varies. We see that in LBT as the priority is increased the performance improves and the dispersion decreases; this is not so for WiFi, where, although the average follows a linear progression, the dispersion is maintained. This fact means that priorities' selection influence LBT performance more than WiFi traffic due mainly to two factors: (1) a lower use of the channel as fewer MCOTs are needed; and (2) a higher probability of collision when the contention window and the MCOT are reduced, especially between distant LBT stations as they are synchronized at subframe level [13]. Such phenomenon is proved in Figure 9 which shows how changes in LBT contention window (indicating a collision) imply a very similar lost packets pattern. Unlike what happens in WiFi where collisions are measured based on the number of retransmissions made, it can be seen that a similar behavior is practically maintained (accutuated for Priorities 1 and 2). Hence, in LBT, lost packets do not depend on the configuration but on the traffic load.  
The fact 3 GPP LBT has the channel for a more considerable amount of time means that, although waiting times are longer in the case of a collision, the transmissions have greater efficiency by having more resources. It is also appreciated in Figure 8(a) that an LBT performance drop (UPT decrease and higher latency values) is produced with Priorities 1 and 2. This adverse effect (especially in Priority 1) is due to a shorter duration of MCOT and short backoff times C\({}_{\text{w}}\), which, in turn, cause an increased number of channel access attempts by WiFi retransmissions. Since WiFi ED-CCA threshold is higher than the one set by LBT (Table 3), such repeated attempts result in a significant increase in the number of collisions produced by the WiFi retransmitted frames causing higher delays in LBT [37]. Nevertheless, in Priority 1, the UPT is constant regardless of the traffic intensity due to a higher probability of accessing the medium but shorter transmission times compared to other priorities.  
Figure 6: User FTP KQI results obtained.  
Figure 7: User Real Time Video Streaming KQI results obtained.  
Figure 8: FTP UPI results obtained.  
Figure 9: MAC/PHY Layer analysis.