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 downlink-uplink (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 E-DCH decoupling allows to compensate the negative impacts of the DL-UL imbalance in HSPA HetNet and achieve efficient system operation.