E-DCH Decoupling for Downlink-Uplink Imbalance Mitigation in HSPA Heterogeneous Networks

This paper considers Universal Terrestrial Radio Access (UTRA) High Speed Packet Access (HSPA) Heterogeneous Networks (HetNet). A problem of the downlinkuplink (DL-UL) imbalance is explored which consists in serving the UL transmission by the strongest Node B in DL not being the strongest one in UL. This causes UL system capacity degradation as well as gives rise to potential problems with inter-cell interference control. The analysis performed in the paper demonstrated that the Soft Handover (SHO) mechanism available in HSPA and assuming simultaneous reception of the UL signal by a set of Nodes B, though not designed intentionally, can partially mitigate the DL-UL imbalance impact. However, some additional aspects of the problem remain such as the scheduling information reception reliability deterioration leading to inability to perform efficient UL scheduling. A novel method of the Enhanced Dedicated Channel (E-DCH) decoupling intended for comprehensive resolution of the DL-UL imbalance problems is proposed. The method consists in moving the UL serving cell functionality for users in SHO between a macro Node B and a Low Power Node (LPN) to the LPN, while keeping the DL serving cell functionality at the macro Node B. System level simulation results provided in the paper demonstrate that the EDCH decoupling allows to compensate the negative impacts of the DL-UL imbalance in HSPA HetNet and achieve efficient system operation.