# Proof-of-Concept of a Millimeter-Wave Integrated Heterogeneous Network for 5G Cellular
## 4 Proof of Concept Implementation and Integration
### PoC Applications  
Two applications were selected to showcase the benefits of the mmWave-integrated cellular networks proposed by MiWEBA: \"Context Aware Caching\" and \"Small Cell On/Off\". The setup for \"Context Aware Caching\" is shown in Figure 16. It comprises a dual-connectivity user device, a macro base station (LTE eNB) and an mmWave small cell (mmWave AP). The client runs a video streaming application while on the move. A context aware cache entity, lying as a middle layer between the video application and the network connection, performs the data requests, using the connectivity status (mmWave connection available or unavailable) as context information. The video file (served as multiple small chunks in Hypertext Transfer Protocol Live Streaming (HLS) format) is fetched from the content server and made available to the video player. When within the coverage of an mmWave small cell, the cache pre-fetches and stores the video file chunks locally at the maximum achievable rate. For this purpose, the cache creates a database of all chunks in the currently playing video. A status is associated with each chunk indicating whether it is locally available, currently downloading or not locally available. The most recently played chunk is stored as a pointer and used to decide which chunk is downloaded next. When outside the range of a small cell, the cache fetches the content on a just-in-time basis to reduce the load on the LTE link. From the user's perspective, the content is available seamlessly. We demonstrated [70] \"Context Aware Caching\" by using the PoC and confirmed that the downloading rate was boosted dramatically while an mmWave link was available. The second demonstration of PoC was the ability to control and optimize the operation of the network resources in terms of energy efficiency by using the developed multi-RAT CP [71; 72]. The centralized RAN (C-RAN), which is LTE eNB in this case, processes context information on its mmWave small cell base stations, including the number of connected user devices and their traffic demand. Depending on the load situation, the C-RAN turned off small cells via the multi-RA CP to save energy. As the user devices were always connected to the CP, the small cells could be immediately reactivated to meet traffic demand. Figure 17 shows a snapshot of small cell on/off and its energy efficiency. This is a result of a system level simulation of the mmWave-integrated cellular networks; however, the function used in this simulation can be realized by the PoC hardware shown in Section 4.1. The left of Figure 17 shows the status of small cell on/off, and the right shows the energy efficiency of the network measured by (bps/W). In the left, the distribution of UEs (blue circles) is not uniform, and there are several hotspots whose locations change in space and time. In this application, the C-RAN implemented in LTE macro eNBs (indicated by yellow stars in the figure) collects traffic demands from UEs. Based on this information, the C-RAN dynamically controls the status of small cell BSs as on (filled red circle) or off (unfilled red circle) to maximize the energy efficiency. In the case of on, the C-RAN immediately switches the UP to small cell BSs as described in Section 4.1. The right of Figure 17 shows the realized energy efficiency by changing time in a day. The performance is calculated with two different frequencies of 60 GHz and 3.5 GHz. Since the coverage (footprint) of  
Figure 16: Caching PoC demonstration. 60 GHz is much smaller than 3.5 GHz, there is higher impact of small cell on/off in 60 GHz (purple line) than 3.5 GHz (green line). It is also clear that the performance of energy efficiency maximization (purple line) in the 60-GHz band has much better performance in terms of energy efficiency compared to that of system rate maximization (yellow line) in 60 GHz without the control of small cell on/off.