Research On Signal Detection For Downlink Non-orthogonal Multiple Access

With the rapid growth of the demand for wireless network applications, the new generation of mobile communication system 5G needs to provide users with higher spectrum efficiency, larger capacity and faster speed network in the future. Faced with the tough challenges of the future, the traditional multiple address technique is no longer applicable, so the industry proposed a new multiple access technique, NOMA(Non Orthogonal Multiple Access). The essence of NOMA is to superpose multiple signals in the power domain before transmitting them. Due to the introduction of the interference signals at the transmitting terminal, therefore how to realize the detection of user signals will be the key to the application of NOMA technology. And the focus of the thesis is the signal detection technology of downlink NOMA.This paper states the basic idea of NOMA firstly, and then introduces the signal detection technique of its downlink, including the basic structure of SIC(Successive Interference Cancellation) detection receiver and the basic principle of signal detection algorithm, such as soft demodoulated, adopted in the receiver, and analyzes its defects.Soft demodulation-SIC is a kind of signal detection method with better performance,but the complexity and delay of the receiver is relatively high. Considering the soft demodulation algorithm doesn’t make full use of the signal feature information of other users’ signal, this paper proposes a joint detection algorithm based on improved soft demodulation algorithm, and this algorithm directly utilize the joint constellation of multiuser superimposed signal to calculate soft information of user signal information bits,don’t need to detect and reconstruct the interference signal, and therefore it can reduce the computational complexity and processing delay of the receiver. Through simulation analysis, the detection method can reduce computational complexity by half and delay by63% under the circumstance of the performance loss of no more than 2dB during the process of detecting user signal of cell proximal for the scene with less link superposition users and user signals using low-level modulation, as compared with the soft demodulation-SIC detection method.For the scene with more link superposition users and user signals using high-level modulation, since the construction and analysis of joint constellation are more difficult and the joint detection method is difficult to detect user’s signal, and what’s more, thedelay of SIC detection technology is relatively large, so this thesis put forward a improved joint detection-interference cancellation method based on SIC detection technology. Each level of the detection method using joint detection algorithm to complete the detection of multiple interference signals, and then eliminate these signals in parallel, which can reduce the processing delay of SIC detection receiver. Through simulation analysis, the detection method can reduce the delay by 33.8% only with 2.5dB loss of detection performance during the process of detecting user signal of cell proximal, as compared with SIC detection method.