Efficient CQI Estimation for Synchronized ABS Configuration in HetNet

In Heterogeneous Networks (HetNets), User Equipments(UEs) in pico cells may suffer from significant co-channel interference from macro stations. The 3rd Generation Partnership Project (3GPP) organization has proposed the concept of Almost Blank Subframe (ABS) so as to reduce the interference of macro stations to pico UEs. Addressing the problem that the introduction of ABS makes it impossible for pico UEs to correctly obtain channel conditions on different subframes, this paper proposes an efficient scheme based on a variable parameter Lambda report and Lambda estimation to derive Channel Quality Indicator (CQI). The method is applicable to the ABS and non-Almost Blank Subframe (non-ABS). It compensates the non-restricted measured CQI with different offsets, based on ABS density and ratio of interference levels from macro cells and pico cells to obtain CQI on different subframes. Simulation and analytical results show that our proposed scheme can achieve approximately 59% gain over the 3GPP system and reduce report overhead significantly without inducing penalties on throughput.