Flow Control for Multiflow in HSPA+

Multiflow is a major enhancement envisioned as part of evolved HSPA. As 3GPP Release 11 is nearing its conclusion, Multiflow forms an integral element of the new set of standards. 3GPP compliant simulation studies from various stakeholders have shown a cell- edge throughput gain in the order of 40%. 3GPP simulation assumptions for Multiflow in release 11 however targeted an ideal scenario to quantify upper bound on achievable throughputs. Some of the key challenges related to Multiflow that have been identified as part of 3GPP work item include flow control between RNC and participating nodeBs, scheduling and distribution of data among the links, dynamic buffer management and the skew arising from an imperfect data split. Although, these issues have been widely discussed in the 3GPP context, there have been no extensive system level simulations so far to accurately study the constraints. This paper highlights such aspects by means of system level simulations. The paper also presents a framework for dynamic buffer management with flow control and the performance of different data split algorithms to combat skew. A comparison of the achievable throughput when an ideal data split is replaced with a realistic one is also investigated.