Hetnets - a new paradigm for increasing cellular capacity and coverage Guest Editorial

Wireless data traffic has been increasing exponentially in recent years. Driven by a new generation of devices (smart phones, MIDs, netbooks, etc.), capacity demand increases faster than spectral efficiency improvement, particularly at hotspots/areas. Also, as services migrate from voice centric to data centric, more users operate indoors, which requires increased link budget and coverage extension to provide uniform user experience. Traditional networks optimized for homogeneous traffic face unprecedented challenges to meet the demand cost effectively. Most recently, Third Generation Partnership Project (3GPP) Long Term Evolution (LTE)-Advanced has started a new study item to investigate heterogeneous network (HetNet) deployments as an efficient way to improve system capacity as well as effectively enhance network coverage. Unlike traditional heterogeneous networks that deal with the interworking of wireless local area networks and cellular networks, which the research community has already studied for more than a decade, in this new paradigm in the cellular network domain, a HetNet is a network containing nodes with different characteristics such as transmission power and radio frequency (RF) coverage area. Low-power micro nodes and high-power macro nodes can be maintained under the management of the same operator. They can share the same frequency band, provided by the operator. In this case, joint radio resource/interference management needs to be provided to ensure the coverage of low-power nodes. In some other cases, the low- and highpower nodes can use discontinuous bands of an operator separately (e.g., through carrier aggregation) so that strong interference with each other can be avoided. Macro network nodes with large RF coverage areas are deployed in a planned way for blanket coverage of urban, suburban, and rural areas. Local nodes with small RF coverage areas aim to complement the macro network nodes for coverage extension or throughput enhancement. In addition to this, global coverage can be provided by satellites (macrocells) according to an integrated system concept. The objective of Het-Nets targets the improvement of overall capacity as well as a cost-effective coverage extension and green radio solution by deploying additional network nodes within the local area range, such as low-power micro/pico network nodes, home-evolved Node-Bs (HeNBs)/closed subscriber group (CSG) cells, and femto and relay nodes.