This paper presents a low complexity bit-level iterative tree search (ITS) detector for Turbo-MIMO wireless communication systems. When combining natural binary bit mapping and QR decomposition on the augmented channel matrix with the symbol-level ITS, we get a bit-level ITS algorithm. In this algorithm the metric is computed in a bit-by-bit fashion. In this way the computational complexity of metric updating and sorting can be greatly reduced. Based on the bit-level ITS, the complexity can be further reduced using the a priori information from the decoder. Because the rank of the augmented channel matrix is always equal to the number of transmitting antennas, the algorithm can work well in an ill-conditioned channel. Simulation shows that the proposed algorithm can achieve similar performance to that of the ITS using natural binary bit mapping and has about 1dB gap with the ITS using Gray bit mapping. In the high SNR region, the complexity of the proposed bit-level ITS is about 6％~40％ of the symbol-level ITS.
