## 6 Results and Discussion  
Figures 6-8 show each evaluation metric versus total offered load, respectively. From Figure 6, Mono-IPT achieved the best system throughput performance and its improvement is 22.0% compared to the conventional scheme with dual channel. Although the previous scheme outperforms the single channel case, it is still worse than other dual channel schemes. Obtained result implies that the proposed approach can fully exploit frequency resources. Throughput of Dual-IPT gradually increases as offered load but it cannot reach for Mono-IPT. What is worse, as the average delay performance shows in Figure 7, delay value of Dual-IPT shoot up in smaller offered load than the conventional scheme. This cannot be the best solution from the delay viewpoint. Mono-IPT also exhibits improved  
Figures 9-11 focused on system throughput, average packet delay and packet loss rate performances for each channel, respectively. As for Figures 9 and 10, curves of the conventional scheme for each channel exhibited the same tendency, they coincide. With Mono-IPT, all metrics can be significantly improved in Ch.1 in which RR-IPT applied carrying only downlink traffic. Due to its enhanced capacity in Ch.1, downlink traffic load input to Ch.2 is reduced and the saturation point can be shifted to larger total offered load. It indicates that packets can be forwarded in reduced delay as far as input traffic reaches saturation point. Its tendency can also be confirmed from delay characteristics in Figure 10. As shown in Figure 11, packet loss rate of Mono-IPT in Ch.2 slightly increases compared to the conventional scheme. Since Ch.2 accommodates bi-directional traffic by CSMA/CA, the collision probability has been increased. RR-IPT can almost eliminate packet loss in Ch.1 and it contributes to improving the whole packet loss rate.  
As a result, Mono-IPT is effective at improving overall system performance regarding both throughput and packet loss rate, notwithstanding employs CSMA/CA in partial channel. Dual-IPT faces limitation in Ch.2 wherein delay performance is deteriorated due to the non-negligible overhead of bi-directional traffic handling by IPT. It obstructs the fine feature of uni-directional IPT in Ch.1. Nevertheless, Dual-IPT can achieve significantly reduced packet loss rate and thus it is applicable in lower traffic situations. We can conclude that the solution is to switch RR-IPT based packet scheduling according to the offered traffic load. This can be performed by observing packet buffer filling level of the core node. This hybrid scheme can realize highly efficient MWBN in terms of both the communication quality and the system capacity. In the case of lower demand traffic, Dual-IPT is applied in order to realize an extremely reduced packet loss rate. When offered load grows, forwarding scheme is switched to Mono-IPT which can enhance the system capacity.  
Although we employed simple IEEE802.11a standard, our approach can effectively work even in recent standards such as 802.11n/ac/ax. To assess the superiority provided by the modified function under the unified/fair constraint, MWBN based on 802.11a with CSMA/CA was sufficient as disclosed above. Of course recent extensions of 802.11 such as short guard interval (GI), aggregated MAC protocol data unit (A-MPDU), and multiple-input multiple-output (MIMO) functions can provide further enhanced throughput. The practical system has some limitations or uncertainty such as jitter, buffer upper limit, packet loss due to the channel conditions. Our future work should set up or introduce the above limitations into simulations via experiment.  
Figure 9: System throughput for each channel.