Optimising wireless access networks Mobile operators are devoting efforts to extending radio coverage to indoor areas, bringing the wireless network closer to its users. However, the installation of small base stations inside buildings may reduce the overall performance of the network if proper indoor network planning is not foreseen. Digital Economy © Thinkstock In the near future, a large part of the access network will get a wireless makeover. It is estimated that nearly 70 % of voice and over 90 % of data services using wireless communications take place indoors. Femtocells — low-power radio access nodes — provide in-building wireless service and may offer some relief for capacity issues.While femtocells provide a host of benefits in terms of coverage improvements and high mobile data rates, these benefits could be negated if the overall performance of the network is reduced due to interference with macrocells. The EU-funded project 'Combined indoor/outdoor wireless network planning' (CWNETPLAN) was designed to study the interactions between indoor femtocells and outdoor macrocells. This will help evaluate and minimise interference that could threaten the outdoor macro network.Project partners first proposed a propagation model to compute the outdoor-to-indoor signal strength and evaluate the interference between outdoor and indoor cells. This model was based on a combination of the intelligent ray launching (IRLA) and the multi-resolution frequency domain parflow (MR-FDPF) models.The idea behind the combined approach was to link the two simulation models by using IRLA outdoors as input for MR-FDPF indoor radio coverage simulation and vice versa. New techniques were applied to convert the outdoor signal at the border of the building into source flows that could be used for the indoor model. With the help of the space-alternating generalised expectation-maximisation (SAGE) algorithm, the team then converted the source flows into rays for indoor MR-FDPF coverage.Another task was to optimise indoor network planning and mitigate the interference that femtocells cause in macrocells. For this reason, a combined optimisation method was required to maximise network performance. Novel resource management schemes were introduced using hybrid femtocells. Finally, to better fit the real environment, the radio propagation models were calibrated.Interference is a key issue associated with femtocell development. CWNETPLAN contributed to finding solutions to ensure that their deployment in indoor environments will take place successfully. Keywords Radio coverage, signal strength, indoor network, wireless, femtocells, macrocells, network planning