From homogeneous to heterogeneous networks: A 3GPP Long Term Evolution rel. 8/9 case study

Heterogeneous cellular networks (HetNets) - conventional macro base stations overlaid with low-power nodes-are being deployed for reasons of improved spectral efficiency, economy, and scalable network expansion. To optimally realize the benefits of HetNets, it is crucial to factor deployment aspects such as cell association, transmission power, spectrum allocation, and deployment density. This paper presents comprehensive dynamic system level simulations based on the 3GPP Long Term Evolution (LTE) standard modeling spatial, temporal, and frequency domain channel variations and ray-tracing based penetration losses in urban and indoor environments. The simulator takes into account the dynamic (subframe level) modulation and coding scheme and precoder selection, as well as finite rate channel state feedback and transmission aspects intrinsic to LTE. Considering a Rel. 8/9 LTE HetNet, two access schemes are analyzed: first, open access picocells, where results show that a single picocell can double the area spectral efficiency without any impairment of the macro-layer, and second, closed access femtocells, where results show that in typical scenarios, the user throughput is deteriorated on both the macro-layer and the femto-layer. Consequently, open access low-power nodes can be deployed as is, whilst closed access ones require additional interference avoidance mechanisms. These dynamic system level simulations are important for deriving accurate and practically relevant performance trade-offs, while commensurate with the time and frequency granularity of LTE.