HetNet Jump-Starts Mature LTE Commercialization

A report published by the Global mobile Suppliers Association (GSA) in October 2011 confirms that, to date, 35 LTE networks have been commercialized in 21 countries, and 248 operators in 87 countries are now investing in LTE. 185 operators worldwide have committed to LTE, and 63 operators worldwide are conducting pre-commitment trials. The GSA also forecasts that at least 103 LTE networks will be in commercial service by the end 2012. However, some problems have emerged with the large-scale deployment of LTE.

• Most LTE networks operate at high frequency bands and have large signal attenuation and penetration loss. This results in poor indoor coverage and even blind spots.
• Data traffic has continued to grow but is distributed unequally. Insufficient capacity is a problem in urban hotspots and in densely populated areas where data traffic is heavy.
• Macrocell deployment puts high requirements on base station sites. Site acquisition is a big challenge in dense urban areas.

To address these issues, heterogeneous network (HetNet) is introduced in 3GPP. HetNet means low-power nodes (LPNs) are placed throughout a macrocell layout (overlaid) and also different layers are coordinated. In a HetNet, a macro network served by high-power base stations provides the foundation for wide area coverage. LPNs, including microcells, picocells, femtocells/home eNBs (HeNBs), and relay nodes (RNs), are designed for incremental capacity growth, eliminating coverage holes, richer user experience and indoor coverage. LPNs have the following features:

• Microcells or picocells are usually centrally deployed, and serve several dozen users within a radio range of 300 m or less. They have a typical transmit power range of 23 to 30 dBm and are mainly used for capacity as well as outdoor or indoor coverage infill in environments where there is insufficient macro penetration, such as bus/train stations, airports, underground parking, and office buildings.
• Femtocells, also known as home eNBs, are low-cost, low-power user-deployed access points that provide blind spot or hotspot coverage in homes or small business environments. Typically, the femtocell range is less than 50 m, and the femtocell’s transmit power is less than 23 dBm. Femtocell terminals support plug-and-play.
• Relay nodes connect with macrocells via radio links. They are positioned to increase signal strength and help operators cheaply expand network coverage. They can be also used for temporary network deployment and to provide limited coverage in high-speed scenarios.

Compared to a traditional homogeneous network comprising a single layer of macrocells, HetNet small cells are deployed in large numbers and are overlaid with macrocells. This presents new challenges for interference elimination, self-organizing network (SON), network management, traffic offloading, and user equipment (UE) mobility. Because coverage overlaps between LPNs and macrocells in a HetNet, intercell interference is more difficult to control than in a homogeneous network, and the interference also changes as a UE moves between macrocells and LPNs. To reduce or eliminate intercell interference, several new techniques have been introduced in LTE-Advanced networks, including TDM-based enhanced intercell interference cancellation (eICIC) with ABS configuration, FDM-based carrier aggregation (CA) with cross-carrier scheduling, and MIMO-based coordinated multi-point (CoMP) transmission and reception.

HetNet is based on a mixed deployment of macrocells and LPNs, which facilitates large-scale and mature commercialization of LTE networks. With multilayer coordination, HetNet addresses coverage issues for indoor areas, blind spots, and high-speed scenarios and enhances system capacity in hot spots. HetNet provides a seamless network experience, and users can enjoy high-speed communication anywhere and anytime.

ZTE has been developing a series of LTE base stations. ZTE’s LTE macro base stations include distributed base stations, indoor macro base stations, and outdoor macro base stations for various deployment scenarios. ZTE has collaborated with CSL Hong Kong and Hutchinson Sweden to commercialize these base stations. In June 2011, ZTE unveiled the world’s first commercial LTE micro base station. The base station is small, lightweight, and easy to install. It supports AC/DC power supply and all frequency bands for LTE. It can be quickly and cheaply deployed in hotspot areas. ZTE has also been developing femtocells, picocells, and relay nodes. With a full series of LTE products and an end-to-end HetNet solution, ZTE is well-positioned to meet operator LTE needs in different scenarios and to strengthen the core competitiveness of operators.