In this paper, we present a low and variable computation complexity decoder based on K-Best for uncoded detection in spatially multiplexed MIMO systems. In the variable complexity K-Best (VKB), the detection of each symbol is carried out using only a symbol constellation of variable size. This symbol constellation is obtained by considering the channel properties and a given target SNR. Simulations show that the proposed technique almost matches the performance of the original K-Best decoder. Moreover, it is able to reduce the average computation complexity by at least 75% in terms of the number of visited nodes.

The development of high data rate wireless communications systems using Multiple Input — Multiple Output (MIMO) antenna techniques requires detectors with reduced complexity and good Bit Error Rate (BER) performance. In this paper, we present the Semi-fixed Complexity Sphere Decoder (SCSD), which executes the process of detection in MIMO systems with a significantly lower computation cost than the high-performance/reduced-complexity detectors: Sphere Decoder (SD), K-best, Fixed Complexity Sphere Decoder (FSD) and Adaptive Set Partitioning (ASP). Simulation results show that when the Signal-to-Noise Ratio (SNR) is less than 15dB, the SCSD reduces the complexity by up to 90% with respect to SD, up to 60% with respect to K-best or ASP and by up to 90% with respect to FSD. In the proposed algorithm, the BER performance does not show significant degradation and therefore, can be considered as a complexity reduction scheme suitable for implementing in MIMO detectors.