LTE Advanced: 3GPP Solution for IMT-Advanced

14.4 Multiflow Transmission

WCDMA Release 99 uses soft handover to improve the quality of the connection at the cell edge and to minimize the inter-cell interference. Soft handover is used also with HSUPA to control the uplink interference. But HSDPA was designed with single cell transmission without any soft handover. The single cell transmission makes the scheduling and fast retransmission control simple but the challenge is that cell edge users experience high inter-cell interference which limits the data rates. One approach to enhance the cell edge data rates is to transmit the data stream from two cells to one UE. This approach is called multiflow HSDPA transmission. The multiflow concept is illustrated in Figure 14.8. Multiflow can be upgraded to the network without any changes to the architecture since HSPA networks already include RNC that can act as the control point for the multiflow transmission. Multiflow is part of 3GPP Release 11.

Figure 14.8 Multiflow transmission concept.

Release 11 allows using multiflow together with dual cell HSDPA: the data will be sent from two separate sectors/base stations and up to four cells (up to two carriers) towards one UE. The multiflow can be done from multiple cells of the same site (intra-site multiflow) or from multiple sites (inter-site multiflow). In the intra-site case the data is split at NodeB in MAC layer and NodeB can run ...