Search sequence determination for tree search based detection algorithms

Tree search based detection algorithms provide a promising approach to solve the detection problems in MIMO systems. Depth-first, Breadth-first or Metric-first search strategies provide near max-log detection at reduced but still significant complexity. In this paper we show how the incurred complexity can be reduced substantially. In order to reduce the number of metric calculations to a minimum, we propose a novel relative determination of search sequences for QAM constellations, usable inexpensively independent of the underlying constellation size and search strategy and moreover also usable for soft-in soft-out detection. Based on its application to a sphere detector, we will demonstrate the impact on complexity and performance of the detection as well as on the detector structure. Building on the results, we propose refinements of the resulting detector providing a very good performance at minimized complexity, making the resulting detector particularly favorable for implementation.