.e., inter-eNB interface) was used as a starting point. In small cell enhancements, both sparse and dense small cell deployments were considered. In some scenarios (e.g., indoor/outdoor hotspots), a single or multiple small-cell node(s) are sparsely deployed to cover the hotspot(s), whereas in other Digital subscriber line is a family of technologies that are used to transmit digital data over telephone lines. The asymmetric digital subscriber line is the most commonly used type of digital subscriber line technology for Internet access. The xDSL service can be delivered simultaneously with wired telephone service on the same telephone line since digital subscriber line uses high-frequency bands for data transmission. On the cus- tomer premises, a digital subscriber line filter on each non-digital subscriber line outlet blocks any high- frequency interference to enable simultaneous use of the voice and digital subscriber line services. 5G Network Architecture 49 scenarios (e.g., dense urban, large shopping mall, etc.), a large number of small-cell nodes are densely deployed to support high-volume traffic over a relatively wide area covered by the small-cell nodes. The coverage of the small-cell layer is generally discontinuous between different hotspot areas. Each hotspot area is typically covered by a group of small cells or a small cell cluster. Furthermore, future extension or scalability of these architec- tures is an important consideration. For mobility or connectivity performance, both sparse and dense deployments were studied with equal priority. Network synchronization is an important consideration where both synchronized and unsyn- chronized scenarios should be considered between small cells as well as between small cells and macro-cell(s). For specific operational features such as interference coordination, carrier aggregation, and coordinated multipoint (CoMP) transmission/reception, small-cell enhance- ments can benefit from synchronized deployments with respect to small-cell search/mea- surements and