Designated non-serving HS-DSCH cell

Description

The designated non-serving HS-DSCH cell is a concept in 3GPP specifications 25.308 and 25.331, introduced in Rel-12. It refers to a non-serving HS-DSCH cell from which the UE estimates the F-DPCH (Fractional Dedicated Physical Channel) quality for TPC (Transmit Power Control) derivation, when the UE is configured with DPCCH2 in the uplink or the Serving E-DCH cell decoupling is configured. This TPC is transmitted on the UL DPCCH (Uplink Dedicated Physical Control Channel). The term is specific to HSPA (High-Speed Packet Access) evolution, particularly for multi-cell and multi-flow operation.

In HSPA networks, the HS-DSCH (High-Speed Downlink Shared Channel) carries user data in the downlink. In multi-cell HSDPA (e.g., Dual-Cell or Multi-Cell HSDPA), the UE may be served by multiple cells, but only one is the serving HS-DSCH cell. The other cells are non-serving. When the UE is configured with DPCCH2, which is an additional uplink DPCCH for improved power control, or when Serving E-DCH cell decoupling is configured (allowing the uplink serving cell to differ from the downlink serving cell), the UE needs to derive TPC commands from a non-serving cell to manage uplink power. The designated non-serving HS-DSCH cell is the specific cell chosen for this purpose. The UE estimates the quality of the F-DPCH from this cell and generates TPC commands, which are then sent on the UL DPCCH to adjust the transmit power of the uplink channels.

The F-DPCH is a downlink channel that carries TPC commands for multiple UEs, introduced in Rel-6 to save code resources. By estimating its quality, the UE can determine the appropriate uplink power. The designated non-serving HS-DSCH cell is configured by the network via RRC signalling (25.331). This mechanism ensures that even when the uplink and downlink serving cells are decoupled, the UE maintains proper power control, avoiding interference and ensuring reliable uplink transmission.

The introduction of this term in Rel-12 aligns with enhancements like Uplink Transmit Diversity and Multi-Flow HSDPA. It allows for more flexible network deployments, such as heterogeneous networks with multiple cells, and improves uplink performance in scenarios where the best downlink cell is not the best uplink cell. The definition has remained stable through Rel-19, indicating its continued relevance in HSPA networks, which are still deployed globally.

In summary, the designated non-serving HS-DSCH cell is a key enabler for advanced uplink power control in multi-cell HSPA. It allows the UE to derive TPC from a non-serving cell when specific configurations are active, ensuring robust uplink communication. Engineers working on HSPA network optimization or UE modem design must understand this concept to configure and troubleshoot multi-cell operations.

Purpose & Motivation

The designated non-serving HS-DSCH cell was introduced to address the challenges of uplink power control in advanced HSPA configurations, particularly when the uplink serving cell is decoupled from the downlink serving cell or when DPCCH2 is used. In traditional HSPA, the serving HS-DSCH cell also handled uplink power control via the F-DPCH. However, with features like Serving E-DCH cell decoupling (introduced in Rel-11/12), the uplink serving cell could be different from the downlink serving cell, creating a need for the UE to derive TPC from a non-serving cell. Additionally, DPCCH2 required a separate power control loop. The designated non-serving HS-DSCH cell provides a standardized mechanism for the UE to estimate F-DPCH quality from a specific non-serving cell and generate TPC commands. This solves the problem of maintaining proper uplink power in heterogeneous networks and multi-cell deployments, where the best downlink cell may not be the best uplink cell. It improves uplink coverage and reduces interference, enhancing overall network performance. The term was introduced in Rel-12 as part of the continued evolution of HSPA to support higher data rates and more flexible deployments.