e percentage of users whose data rate is below 10 Mbps. These users are considered to be in outage. The number of users with below 10 Mbps is significantly reduced from 12% to 5% with 200 Wi-Fi cells in a 1 km2 area. An alternative would be to deploy more indoor Wi-Fi cells and fewer outdoor cells as shown with an example of 1700 Wi-Fi and 100 micro cells. The split between outdoor and indoor cells depends on which one is the most cost-efficient solution. It has been shown that similar performance can be achieved by deploying indoor femto cells. Indoor LTE femto cells tend to be simpler from the interference point of view compared to the outdoor small cells. In-band deployment is the default option due to operators having Users with <10 Mbps data rate Micro Macro 200 micros 100 micros 200 micros No Wi-Fis 1700 Wi-Fis 200 Wi-Fis Figure 5.9 Example of indoor offload via Wi-Fi cells in a dense urban area with 20 macro sites and 200 micro cells LTE Small Cell Optimization limited spectrum resources. Femto cells do not typically have as advanced schedulers as micro and pico cells and the necessary interfaces to coordinate with macro in order to reduce interference. This makes femto cells more suitable for indoor coverage. Femto cells' inability to manage interference means they are not very suited to a high density or large environment that requires very dense deployment or a very large number of cells. The challenges of femto deployment become even more pronounced when a femto cell is configured with a Closed Subscriber Groups (CSG) identity. A user that is not part of the CSG group will connect to the macro network and experience or cause significant inter- ference problems as normal mobility is overruled by the subscriber group admissions. The optimum performance will be achieved by configuring all femto cells as Open Subscriber Groups (OSG). However, femto cells provide excellent voice coverage extensions and the low transmission power and building attenuation isolate the femto cells very well from the macro cells