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For a MIMO downlink system with finite-bit feedback,combined with the Golden code and the precoding technology,a new precoding design criterion and its related codeword selection method,transmissionschemes and corresponding low complexity decoding methods were proposed.In fact,based on fully utilizing the characteristics that the Golden code could overcome the channel depth fading,a double precoding matrix was constructed as transmission signals by using the selected precoding codeword,so that the decoding complexity could be reduced to linear.In the meantime,a joint ML and MMSE decoding method was proposed for the traditional transmission scheme,which could dynamically adjust the decoding complexity based on a threshold.The numerical simulation results confirm the superiority of the proposed schemes and methods.

Objective To compare the efficacy and safety of percutaneous dilational tracheostomy（PDT）using fiberoptic bronchoscope，ultrasound guidance and anatomic landmark localization. Methods In this retrospective cohort，101 patients undergoing PDT were enrolled and divided into bronchoscope-guided group（n = 39），ultrasound-guided group（n = 27），and anatomical landmark localization group（n = 35）. Demographic data，general condition，surgical condition，postoperative complication and clinical prognosis were collected. Results No statistical significance was found in age，sex，cause of ICU stay，primary disease and preoperative coagulation status（all P > 0.05）. In the ultrasound-guided group，preoperative Sequential Organ Failure Assessment（SOFA）score was higher，the operation time was shorter and intraoperative blood loss was less compared with those in the other two groups（P < 0.05/3）. The PaCO2 in the anatomical landmark localization group was lower than that in the ultrasound-guided group（P < 0.05/3）. Conclusions Real-time ultrasound guidance during PDT can be employed to identify the anatomical structures of the neck，which can shorten the operation time，reduce intraoperative bleeding and avoid hyperventilation in patients with severe diseases. Ultrasound-guided PDT may serve as an alternative regimen for PDT using bronchoscope or anatomical landmark localization.