Femtocell Architecture in LTE, WiMAX, and 3G UMTS

Femtocells are small, low-power cellular base stations designed for use in homes, offices, and indoor environments. They enhance network coverage and capacity by providing localized connectivity, bridging gaps in indoor signal quality, and improving overall network performance. Femtocells are deployed to handle low user density, typically covering an area between 10 to 30 meters. While LTE, WiMAX, and 3G networks have different architectural designs, femtocells play a crucial role in each network by improving indoor coverage and reducing load on the macro network. This tutorial explores the architecture of femtocells in LTE, WiMAX, and 3G UMTS networks, including their design, components and role in optimizing indoor coverage and performance.

Femtocell Architecture in LTE Networks

Femtocells in LTE networks are designed to support the high data rate requirements of modern users and enhance indoor coverage by connecting to the network core through an IP backhaul. The architecture typically consists of the following components.
• eNodeB (evolved Node B): The LTE femtocell operates as a small-scale eNodeB, providing radio access to users. It communicates with mobile devices through the LTE-Uu interface.
• HeNB (Home eNodeB): HeNB is the standard term used for LTE femtocells. It connects to the Evolved Packet Core (EPC) through the S1 interface.
• HeNB Gateway: This component aggregates traffic from multiple HeNBs, performing security, mobility, and signaling functions. It communicates with the EPC to provide seamless connectivity and handovers.
• Security Gateway (SeGW): Ensures secure IPsec tunnels between the HeNB and the EPC, protecting data and signaling traffic from unauthorized access.

LTE is defined in 3GPP specifications. It supports OFDMA modulation in the downlink and SC-FDMA modulation in the uplink. It supports FDD and TDD topologies. Based on this, TD-LTE femtocell and FD-LTE femtocell exists. Refer LTE tutorial for LTE system basics and architecture interfaces.

The figure-1 depicts LTE femtocell architecture in E-UTRAN network as per LTE 3GPP specifications. The HeNS(Home eNodeB Subsystem) composed of a HeNB( Home eNodeB ). HeNB-GW is included optionally in the network architecture. As LTE is all packet network. HeNS is interfaced with EPC using S1 interface types. It is interfaced with SGW using S1-U interface and with MME using S1-MME interface.

Advantages of LTE Femtocells

1. Enhanced Indoor Coverage: Overcomes the limitations of high-frequency LTE bands.
2. Capacity Offloading: Reduces the load on macro cells in densely populated areas.
3. QoS Management: Maintains high Quality of Service (QoS) for voice and data services.

Femtocell architecture in 3G UMTS networks

3G femtocells, also known as Home NodeBs (HNBs), are small UMTS (Universal Mobile Telecommunications System) base stations that connect to the mobile operator’s network through a broadband internet connection. The architecture of 3G femtocells includes following.
• HNB (Home NodeB): Provides radio access using the WCDMA (Wideband Code Division Multiple Access) air interface. It supports voice, data, and video services.
• HNB Gateway (HNB-GW): Aggregates connections from multiple HNBs. It ensures that handovers between femtocells and the macro network are seamless and manages signaling and security functions.
• Core Network Connection: The HNB connects to the 3G Core Network (CN) through the Iu interface. It handles control plane (Iu-c) and user plane (Iu-u) traffic separately.

The figure-2 depicts 3G femtocell architecture in UTRAN network as per UMTS specifications. As shown the HNS(Home NodeB subsystem) is composed of HNB(Home NodeB) and HNB-GW(Home NodeB Gateway).

The HNS is interfaced with MSC using lu-CS interface for circuit switched services. The HNS is interfaced with SGSN using lu-PS interface for packet switched services.

lu-h interface is the interface between HNB and HNB-GW. HNB has functionalities of both RNC and NB. Refer UMTS network architecture for more information.

Advantages of 3G Femtocells

1. Enhanced Voice and Data Services: Improves the quality of voice calls and data services in indoor areas.
2. Reduced Network Load: Offloads traffic from the macro network, enabling better performance for both indoor and outdoor users.
3. Seamless Handover: Ensures smooth transitions between femtocell and macro cell coverage without dropping calls.

Femtocell architecture in WiMAX

WiMAX (Worldwide Interoperability for Microwave Access) is a wireless broadband technology that provides high-speed data over long distances. Femtocells in WiMAX networks are designed to offer indoor connectivity with seamless integration into the larger WiMAX infrastructure. The primary components include following.
• Access Service Network (ASN): The femtocell functions as part of the ASN, managing radio resources, handovers, and connectivity. It communicates with user devices using the air interface similar to larger WiMAX base stations.
• ASN Gateway: Aggregates traffic and signaling from multiple femtocells. It is responsible for authenticating devices, managing QoS and enabling mobility management.
• Connectivity Service Network (CSN): Provides IP connectivity, authentication, and accounting services. It connects to external networks like the internet and handles femtocell backhaul.

The figure-3 depicts wimax femtocell architecture in wimax network as per wimax specifications published by wimax forum. As shown wimax femtocell access point(WFAP) is interfaced directly with ISP(Internet Service Provider). This ISP provides broadband connection using DSL, Cable, Fiber or Wireless. Handover is needed between femtocell and macrocell in poor signal conditions.

It is also needed between femtocell to femtocell when user(wimax CPE) goes out of reach of wimax femtocell coverage. In the same way handoff is required in UMTS and LTE networks. Refer wimax network architecture.

Advantages of WiMAX Femtocells

1. Improved Indoor Connectivity: Solves indoor coverage issues by operating on licensed or unlicensed bands.
2. Seamless Integration: Femtocells are managed as part of the existing WiMAX infrastructure.
3. Cost Efficiency: Low-cost deployment with efficient use of network resources.

Comparison of Femtocell Architecture in LTE, WiMAX, and 3G

Conclusion

Femtocells are an essential component for enhancing indoor coverage and performance in cellular networks. While the fundamental concept remains the same across LTE, WiMAX, and 3G, each technology utilizes different architectural approaches and components to achieve seamless connectivity and improved quality of service. Understanding these differences helps network engineers and telecommunication professionals select and deploy femtocells effectively to meet the specific requirements of each network type.

Femtocell related links

RF Wireless Tutorials