Multi-Flow Transmission and Carrier Aggregation Inter-Operation in HSPA+ Advanced

Carrier aggregation and multi-flow transmission are among the most important features of HSPA+. While the former allows users to be served simultaneously by several carriers in the same sector, the latter enables adjacent sectors to simultaneously schedule different data streams to the same user in their overlapping region. In this paper, we investigate the inter-operation of these two features. We evaluate the flow-level performance using a method based on network simulation coupled with Markov chain analysis. Results in single-carrier mode show an improvement in throughput at low load and an efficient load balancing across sectors at high load. In multi-carrier mode, we show that coordination is no more recommended since it does not achieve any throughput gain over the classical multi-carrier system. This is due to the actual status of the standard that limits the number of carriers that can be used for the multi-flow transmission to two. However, if this restriction is released in the standard, our results show that multi-flow transmission would bring significant gains.