Congestion Control in Evolved HSPA Systems

Evolved HSPA is a major evolutionary step of the WCDMA based 3GPP technology that provides high end user data rate and increased cell throughput. It can be deployed over the legacy 3G architecture, but an alternative packet based, flat architectural solution is introduced too, that enables the later transition to LTE. Smooth transition requires that the new, flat systems are first deployed as complementary solutions of the existing infrastructure. This will lead to heterogeneous radio systems that will be served by a shared packet based transport network. This co-existence raises fairness issues as transport congestion is handled differently by legacy and flat systems in addition to the fact that due to Radio Layer 2 protocol aspects, the Iub traffic is not TCP friendly. This paper discusses the architecture of the heterogeneous systems, the fairness problem in case of congestion on shared transport links and proposes a congestion control mechanism that is able to enforce fair resource usage. The solution is evaluated with simulations.