# Optimization of Pico-eNB Tx Power and the Effects of Picocell Range Expansion in Multiband HetNet
## 6 Conclusions  
In this paper, we first investigated the optimal Tx power for pico-eNBs in a multiband HetNet combining macrocells operating at a 2 GHz band and picocells with a 10 times wider signal bandwidth operating at a 4.5 GHz band. Specifically, we presented the average and 5-percentile user throughput as a function of the pico-eNB Tx power using system-level computer simulations. It was observed that the average user throughput increased as the Tx power increased up to approximately 37 dBm. However, Tx powers greater than 37 dBm slightly degraded the average user throughput. Consequently, it was concluded that a pico-eNB Tx power of 37 dBm was able to provide the best performance from the average user throughput perspective, under the HetNet model as shown in Table 1. Furthermore, we analyzed the use rate of each modulation method used in the downlink MCS incorporating 1024-QAM as a function of pico-eNB Tx power. The use rates of both 256- and 1024-QAM were at a maximum when the pico-eNB Tx power was 37 dBm, although the use rate difference for the pico-eNB Tx power was very small. Then, we described the effects of picocell range expansion (CRE) technique using a positive CSO for two pico-eNB Tx powers close to the optimal value. We demonstrated the average and 5-percentile user throughput as a function of CSO for two pico-eNB Tx powers close to the optimal Tx power (i.e., 31 and 37 dBm). When the CRE was activated, it was shown that a CSO of 6 dB was able to provide the best performance when the pico-eNB Tx power was 31 dBm. When the pico-eNB Tx power was 37 dBm, the CRE did not work and that it had no effect on improving the average user throughput. In other words, the average user throughput for a pico-eNB Tx power of 31 dBm and CSO of 6 dB was almost the same as that obtained with a pico-eNB Tx power of 37 dBm and a CSO of 0 dB. Consequently, it was clarified that the CRE technique could reduce the pico-eNB Tx power in multiband HetNet. This will lead to saving the power consumption of pico-eNBs while maintaining the average user throughput. Conceptualization, H.O. and T.Y. ; Investigation, T.Y. and H.O. ; Data curation, T.Y. and K.Y. ; Writing--original draft preparation, H.O. ; Writing--review and editing, H.O. and T.Y. ; Visualization, T.Y. and K.Y. ; Supervision, H.O. ; Project administration, H.O. ; Funding acquisition, H.O. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded by JSPS KAKENHI Grant Number JP21K11874, Grant-in-Aid for Scientific Research (C). **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** Not applicable. **Acknowledgments:** The authors would like to thank [PERSON] who is a graduate of Kogakuin University for her contributions to construct system-level computer simulations. **Conflicts of Interest:** The authors declare no conflict of interest. * [PERSON] et al. (2020) [PERSON]; [PERSON]; [PERSON] Distributed User Association and Resource Allocation Algorithms for Three Tier HetNets. _IEEE Trans. Wirel. Commun._**2020**, _19_, 7913-7926. [CrossRef]
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