Analysis of Interference and Performance in Heterogeneously Deployed LTE systems

Heterogeneous network deployment has been advocated as a mean to enhance the performance of cellular networks, but at the same time heterogeneous deployments give rise to new interference scenarios which are not seen in homogeneous deployments. This report includes five studies pertaining heterogeneous network deployments which is based on simulations of LTE in high detail on the lower layer protocol stack. In the first study it is investigated if results from simulated systems with ideal deployments can be generalized to realistic low power node deployments, which is seen to be the case. Three heterogeneous network con gurations, speci ed by 3GPP, were compared to a macro-only system. It is observed that the gain from low power nodes is strongly connected to the distribution of UEs. If the UE distribution is uniform the UE throughput gain is below 100 % while if the UEs are highly clustered a UE throughput gain of 400 % is achieved. The configuration with uniform UE distribution was further analyzed and it was seen that in a low load system the average UE throughput gain from low power nodes is below 20 %. In a low loaded system with uniform UE distribution adding low power nodes is not a good way of enhancing the system performance. A study investigating the gain of low power node range extension showed that SINR problems arise if the range of the low power nodes is extended, however the system as a whole gets increased throughput. The same applies for UE throughput. The main reasons are macro layer offloading & reduced interference created by the macro layer. It is showed that if more low power nodes are added the UE throughput gain per low power node increases. It is also showed that a system with two range extended low power nodes outperforms a system with four low power nodes without range extension. Inter-low power node interference is seen not to be a problem in the simulated system configurations