Hosseini, S. S.Abouei, J.Uysal, Murat2015-11-032015-11-032015-051536-1276http://hdl.handle.net/10679/1013https://doi.org/10.1109/TWC.2015.2395411Due to copyright restrictions, the access to the full text of this article is only available via subscription.This paper presents a comprehensive study on the problem of decoding complexity in a Multi-Input Multi-Output (MIMO) Hybrid Automatic Repeat reQuest (HARQ) system based on Space-Time Block Codes (STBCs). We show that there exist two classes of fast-decodable MIMO HARQ systems: independent and dependent STBC structures. For the independent class, two types of protocols namely, fixed and adaptive threshold-based are presented and their effectiveness in both computational complexity reduction and spectral efficiency preservation are discussed. For the dependent class, a fast Sphere Decoder (SD) algorithm with a low computational complexity is proposed for decoding process of HARQ rounds. Two new concepts are introduced to leverage the fast-decodable notion in MIMO HARQ systems. Simulation results show that the proposed fast-decodable MIMO HARQ protocols in both classes provide a significant reduction in the decoding complexity as compared with the original MIMO HARQ method.engrestrictedAccessarticle1452827284000035446860003710.1109/TWC.2015.2395411MIMO communicationAdaptive codesAutomatic repeat requestComputational complexityDecodingProtocolsSpace-time block codes2-s2.0-84929346756