# Proof-of-Concept of a Millimeter-Wave Integrated Heterogeneous Network for 5G Cellular
## 2 mmWave-Integrated Cellular Networks
### LTE-WLAN Interworking and Aggregation  
The access network discovery and selection function (ANDSF) [53; 54; 55; 56] is a core-network (CN) function that controls UP data offloading between 3 GPP RATs (e.g., LTE) and non-3 GPP RATs (e.g., WLAN). ANDSF is located in the evolved packet core (EPC), which is part of the 3 GPP CN. ANDSF delivers to the UEs the auxiliary information for RAT discovery and selection on the basis of UE context, such as location or IP flow. On the basis of the delivered policies, the UE selects an appropriate RAT to connect with the network. Figure 3a shows an example of the ANDSF-based LTE-WLAN interworking architecture known as CN-level interworking. In this LTE network, the UE is connected to a base station (BS) called evolved Node B (eNB), via an LTE air interface, which is called a Uu interface (radio interface between the Universal Terrestrial Radio Access Network and the UE). When the traffic from an external packet data network (PDN), for example the Internet, is handled by the Uu interface, the traffic is transferred via the PDN gateway (PDN GW), the serving gateway (S-GW) and eNB to the UE. For offloading the traffic to WLAN, two schemes are available:  
* Non-seamless WLAN offload (NSWO): In NSWO, the traffic is not sent via the EPC, but directly from the Internet to the WLAN-AP. An offloading scheme that bypasses the EPC is called non-seamless WLAN offload (NSWO). In NSWO, the IP flow between the network and UE is interrupted during LTE-WLAN handover, because a different IP address will be allocated to each RAT. In addition, the UE cannot use the operator's private IP services via WLAN. * Seamless WLAN offload: When the UE is capable of IP flow mobility (IFOM), the traffic can be transferred to the UE via the WLAN-AP and a PDN GW, an evolved packet data gateway (ePDG) or a trusted wireless access gateway (TWAG). In this scheme, the UE can offload the same IP flow from LTE to WLAN. The PDN GW is an anchor point between the LTE and WLAN accesses. Figure 2: IEEE 802.11 ad/WiGig communication devices: (**a**) Panasonic® WiGig-USB dongle: 60-GHz antennas, RF, PHY and MAC components are bundled into one package. Universal Serial Bus (USB)-3.0 is used as the interface to higher layer processors, such as a personal computer (PC). (**b**) Intel® Wireless Gigabit Antenna module (top) and Intel® Tri-Band Wireless-AC 17265 WiGig and Wi-Fi + Bluetooth combination module [52] (bottom). The antenna module contains a beamforming phased antenna array (PAA) of 10 \(\times\) 2 elements (8 \(\times\) 2 active elements, 8 in azimuth and 2 in elevation). ANDSF is an efficient and scalable mechanism for controlling the UE behavior of RAT discovery and selection from the network. The UE can be authenticated from both LTE and WLAN networks with a single subscriber identity because the EPC and WLAN can exchange authentication, authorization and accounting (AAA) information via a 3 GPP AAA server. However, ANDSF cannot control UP offloading in a hyper-dense HetNet for two reasons. First, the initial design of Release 8 ANDSF was designed to be a 3 GPP AAA server. Second, the proposed network architecture is a 3 GPP AAA server. The network architecture is a 3 GPP AAA server. intended to provide policies based on a static coverage map [57] and not to be responsive to real-time traffic or radio network conditions. Later releases of ANDSF were extended to provide quasi-real-time statistics, such as RAN congestion. However, it is difficult to handle real-time changes in a dense network because the ANDSF entity is separated from both eNB and WLAN AP in the network. Second, the mobility anchor point (PDN GW) is too distant from the eNB and WLAN AP in the network. Frequent inter-RAT handover in a dense network consequently increases the signaling load in the EPC, which lengthens the handover interruption time. Moreover, the enhanced features deployed in eNB, such as mobile-edge computing (MEC) [58], cannot be used via WLAN access.