On Femto placement and decoupled access for downlink and uplink in enterprise environments

While it is easier to quench the demand for higher data rates outdoors, it is still a significant challenge when it comes to attaining similar data rates for indoor User Equipments (UEs). Femto cells were introduced for this purpose and also to minimize the traffic load on macro Base Stations (BSs) in 4G/LTE cellular networks. Indoor UEs can achieve good throughput if they get high Signal to Noise Ratio (SNR), but the inherent problem of path loss due to obstacles prevents UEs from receiving good signals. So, the efficient placement of Femtos in enterprise buildings is crucial. For the optimal placement of Femtos, we developed a Mixed Integer Linear Programming (MILP) model and solved it using the GAMS tool. Once the network planning is done, the next problem that has to be addressed is the downlink traffic imbalance which happens due to non-uniform UE traffic distribution. Traditionally load imbalance is addressed by transferring some of the UEs from the highly loaded cell to a less loaded neighboring cell but this could increase the UE uplink transmission power as it now connected to a cell which is not the closest one. To improve UE battery life and to boost the downlink throughput, we decouple the uplink and downlink (DuD) access to UEs by connecting the uplink to the shortest pathloss Femto, and the downlink to one of less loaded neighboring Femtos. Our extensive experimentation in MATLAB shows that on average, the decoupled access system achieves 70% energy savings (i.e., uplink power) when compared to coupled access system.