Physical Cell Identity (PCI), PCI Collision and PCI Confusion in LTE

Physical Cell Identity (PCI), PCI collision & PCI confusion JAKIR HOSSAIN

Presentation Outline

PCI Overview

PCI collision

PCI Confusion

Physical Cell Identity (PCI)

3 Physical cell identifiers (PCIs) are used for signal synchronization and random access. Each evolved universal terrestrial radio access network (E-UTRAN) cell is allocated a PCI. There are 504 PCIs in the LTE system. These PCIs are divided into 168 groups, each containing 3 PCIs. (PCI = 3*SSS+PSS) PSS & SSS two synchronization signals transmitted once every 5 ms

Primary Synchronization Signal (PSS) ◦ 3 different sequences called Physical-Layer Identities (0-2) ◦ Subframe #1 and #6 ◦ Mapped on 72 subcarriers in the middle of the band ◦ OFDM symbol #2

Secondary Synchronization Signal (SSS) ◦ 168 different sequences called Physical-Layer Cell-Identity groups (0-167) ◦ Subframe #0 and #5 ◦ Mapped on 72 subcarriers in the middle of the band ◦ OFDM symbol #13

PCI Collision Detection & Self-Optimization •

When many cells exist in an LTE system, some cells must share one PCI. A PCI conflict between neighboring cells may occur if PCIs are planned inappropriately or changed manually, or if neighboring cell parameters are modified.

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To solve this problem, Huawei developed the PCI conflict detection and selfoptimization feature. It helps detect and resolve the PCI conflict between neighboring cells, allocate optimized PCIs to conflicting cells, and therefore reduce service drop rates.

PCI Collision PCI Collision: A PCI collision occurs between two intra-frequency cells that use an identical PCI. In this case, UEs in the overlapping area of the two cells cannot implement signal synchronization or decoding. Figure shows a PCI collision between cell A and cell B.

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PCI Confusion PCI Confusion: A PCI confusion occurs between a detected cell and a neighboring cell if the two cells have the same frequency and PCI and if the reference signal received power (RSRP) of the two cells reaches the handover threshold. The PCI confusion may lead to UE handover failures or service drops.

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If the UE does not support ANR, the eNodeB cannot determine whether the detected cell is cell B or C based on the report by the UE. This may lead to a handover failure. If the UE supports ANR, the eNodeB can identify cell B based on the E-UTRAN cell global identifier (ECGI) reported by the UE. Then, a handover to cell B can be performed if necessary.

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Thank You