Home Technical objectives Enhancements in the access network
Enhancements in the access network

The design of a rural wireless access network is focused on providing voice and data services at a low cost, allowing an easy and progressive network upgrade as traffic demand increases. Little human intervention and reduced energy consumption are required to fit the constraints of the rural scenario. To address these challenges TUCAN3G envisions the provision of affordable and profitable connectivity in rural areas by means of deploying multiple femtocells with a wireless backhaul1.

Specifically, TUCAN3G proposes a scenario where the wireless access network consists of distributing multiple UMTS/HSPA (3G) femtocells (HNB) with a wireless backhaul over given rural areas. On each of these areas, a gateway will be in charge of linking the transport and access network segments, along to properly design the transmissions over the wireless backhaul, which are performed with a different Radio Access Technology (RAT), like WiFi or WiMAX. Provided a reliable transport network, femtocells guarantee all the requirements of rural communications deployments: being inexpensive, sustainable, energy efficient, self-organized and long-term self-sufficient.

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Figure 1. Sketch of the overall network structure

The challenges to be faced in the access network are:

  •     Distributed non-supervised methods for energy consumption optimization under service constraints;
  •     Network monitoring;
  •     Self-organising carrier selection and interference management;
  •     Efficient interoperability with the transport network; and
  •     Core-network data-plane offloading when the traffic in the access network grows.

Nevertheless, the way these challenges are tackled strongly depends on the type of connectivity and technology considered for femtocells. TUCAN3G addresses voice and limited-data connectivity by means of UMTS/HSPA (3G) femtocells, while voice and high-speed data connectivity can be addressed by LTE (4G) femtocells. TUCAN3G proposes 3G technologies to provide mobile voice service to rural areas, while 4G technologies will also be a matter of study in order to know how TUCAN3G concept will evolve beyond the lifetime of the project. When the traffic demand increases, larger volumes of data traffic are an issue and 4G technology becomes affordable.

Femtocells deployments allow updating the access network topology and density in an easy yet unplanned way. However, such unplanned deployment may generate a harsh interference scenario which has to be managed in order to provide large spectral efficiency, low coverage outage and reduced energy consumption. Different strategies that encompass these features will be developed. As a simple example, femtocells might be switched on/off depending on the traffic demands, with the objective of saving energy. Consequently, self-adaptation algorithms must be investigated able to track and react to changes in the network traffic and topology.

The radio resource allocation in the access network should take into account the QoS constraints imposed by the wireless backhaul and defined by the transport network. Both networks (transport and access) work with different radio access technology (RAT) like WiFi, WiMAX or UMTS/HSPA. Although they could be optimized independently, the instantaneous quality of the backhaul will influence the capacity of the access network to provide service. Therefore, it should be investigated the benefits of performing a joint resource allocation, analyzing also the required signaling and computational complexity.

A femto gateway is the network element that connects the TUCAN3G's transport network with the core network of the operator (see Figure above). In order to route local calls among terminals connected to the access Network without intervention of the operator's core network (and hence offloading the transport network), LIPA/SIPTO solutions will be investigated. These will be contemplated and evaluated in terms of reduction of the potential congestion of the transport network (triggered by an eventual mid-term traffic growth), and also from an economical point of view.

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1 Although femto base stations are commonly placed indoors in order to serve indoor users, they can also be used to provide service to all indoor and outdoor users in their vicinity (as it is considered by the Neighborhood Femtocell concept [Qualcomm-2012]).