Analysis of the Influence of PCI Planning on the Physical Uplink Control Channel in LTE

Abstract

In Long Term Evolution (LTE) systems, the physical cell identity (PCI) assigned to a cell during network planning determines the set of sequences used by subscribers as de-modulation reference signals (DM RS) in the uplink (UL). A proper assignment of PCIs must prevent neighbor cells from using the same DM RS to avoid interference problems, thus ensuring adequate performance both in control and user data channels in the uplink. In this paper, a comprehensive analysis is carried out to quantify the impact of PCI planning on the performance of physical uplink control channel (PUCCH) in LTE. First, a novel analytical model that reflects the influence of PCI planning on interference and outage probability due to DM RS collisions in PUCCH is presented. Based on this model, PUCCH performance with several classical PCI planning schemes is evaluated with a static system-level simulator implementing a real network scenario. Simulated cases cover different PUCCH frame formats, different UL power control (PC) schemes and both regular and irregular traffic scenarios. Results show that a PCI plan constructed solely based on avoiding PCI collision/confusion and reference signals collisions in the downlink achieves near-optimal performance in terms of DM RS collisions in PUCCH, but, however, in extreme cases, DM RS collisions caused by neighbor cells sharing the same sequence might degrade PUCCH performance significantly.