Investigation on Rate Matching and Soft Buffer Splitting for LTE-Advanced Carrier Aggregation

In the LTE-Advanced downlink, carrier aggregation (CA) employing multiple component carriers (CCs) is an essential technique to achieve a target peak data rate of 1 Gbps. 3GPP RAN WG1 meeting decided to adopt one transport block (TB) per CC, where the TB is the unit of channel coding and hybrid automatic repeat request (HARQ). When CA is applied to an LTE-Advanced UE, the soft buffer which is used for HARQ packet combining must be equally split according to the number of CCs, where the soft buffer size is one of the factors to in defining the LTE-Advanced UE categories. When soft buffer splitting is applied to UEs in a lower UE category, the soft buffer size per CC may not be sufficient and the performance of the HARQ packet combining is not ensured. In this paper, we propose a rate-matching scheme for CA and a new receiver suited to this rate matching scheme. Using the proposed scheme, degradation in the HARQ throughput performance due to the soft buffer splitting can be avoided and the same rate-matching scheme can be applied irrespective of the number of CCs. Simulations results show that the proposed scheme always provides better performance than that for equal splitting rate-matching scheme that reuses Rel-8 LTE rate-matching scheme.