# Low Power Consumption Signal Detector Based on Adaptive DFSD in MIMO-OFDM Systems
## 1 Introduction  
Wireless communication technology has evolved as demand for increasing the data rate has grown. Multiple input and multiple output (MIMO) based on orthogonal frequency division multiplexing (OFDM) systems can increase the capacity of wireless communication by using multiple antennas, and improve link reliability in transferring data [1; 2; 3]. To maximize these benefits, the design of the receiver is important. The purpose of the receiver is to detect the signal exactly and to reduce the complexity of signal detection. In 5G wireless infrastructure, because the number of antennas and the required data rate has increased, the required power consumption increases rapidly at the signal detector. So, it is needed to lower the power consumption by reducing the complexity. The linear signal detection algorithms of MIMO-OFDM systems are zero forcing (ZF) and minimum mean square error (MMSE) detection schemes [4; 5]. The ZF and the MMSE detection schemes have low complexity. However, the detection performance of these schemes is not good from the bit error rate (BER) point of view. Other types of detection schemes include non-linear detection schemes such as decision feedback equalization (DFE), ordered successive interference cancellation (OSIC) detection schemes, and so on [6; 7]. The DFE and the OSIC detection schemes have better error performance than the ZF and the MMSE detection schemes. In contrast, the complexity of these non-linear detection schemes is high compared to the ZF and the MMSE detection schemes. The optimal signal detection scheme for the MIMO-OFDM systems is the maximum likelihood (ML) detection scheme [8; 9]. However, the complexity of the ML detection scheme is very high when the modulation order or the number of transmit antennas increases. So, many researchers have studied the schemes to detect the signal, having similar error performance and low complexity compared to the ML detection scheme. Moreover, the non-linear detection algorithm using DFSD algorithm wasproposed. The DFSD detection scheme has suboptimal performance compared to the ML detection scheme [10; 11; 12; 13]. Also, the DFSD detection scheme has lower complexity than the ML detection scheme. However, the DFSD detection scheme still has high complexity in the hardware implementation. In order to overcome these disadvantages, this paper proposes an adaptive DFSD detection scheme, which has low complexity compared to the conventional DFSD detection scheme.  
The adaptive DFSD detection scheme uses thresholds based on channel condition to vary the number of top layer nodes of DFSD tree structure. When the DFSD detection scheme uses one node at the top layer, error performance is not good compared to the DFSD detection scheme using full nodes at the top layer. But, the complexity of the DFSD detection scheme using one node at the top layer is lower than the DFSD detection scheme using full nodes at the top layer. In OFDM symbols, if subcarriers suffer from a poorly conditioned channel, full nodes are used at the top layer, like the conventional DFSD detection scheme. But, one node is used at the top layer when the channel has the best condition. In the case of a general conditioned channel, the number of nodes varies depending on the channel condition. By using the proposed method, the adaptive DFSD detection scheme has little error performance degradation and significantly less complexity.