Performance Analysis of Relay Based NOMA Cooperative Transmission under Cognitive Radio Network

This paper proposes a hybrid spectrum accessing mechanism by using NOMA-based cooperative transmission and beam-forming technology.In this mechanism,the secondary user employs spectrum-sensing technology to detect the existence of the primary user.If the primary user does not exist,the secondary source user directly transmits data to the destination user.If the primary user exists,the secondary source user finds the optimal relay according to certain selection principle before transmitting data to the destination user through the chosen relay node.For the signal receiving stage,the secondary user takes use of beam-forming technology to receive the signal from both the secondary source and the secondary relay node.Meanwhile the interference from the primary user is cancelled out in the stage.Furthermore,the outage probability for secondary user in the proposed mechanism is theoretically derived.Finally,the simulation results show that compared with the traditional mechanism,the proposed system model can not only guarantee the continuity of secondary transmission,but also significantly reduce the outage probability of secondary transmission.

Performance Analysis on Output SINR of Robust Two-Stage Beamforming

In this paper, we present a theoretical analysis of the output signal-to-interference-plus-noise ratio (SINR) for eigen-space beamformers so as to investigate the performance degradation caused by large pointing errors. For the sake of reducing such performance loss, a robust scheme, which consists of two cascaded signal processors, is proposed for adaptive beamformers. In the first stage, an algorithm possessing time efficiency is developed to adjust the direc-tion-of-arrival (DOA) estimate of the desired source. Based the achieved DOA estimate, the second stage provides an eigenspace beamformer combined with the spatial derivative constraints (SDC) to further mitigate the cancellation of the desired signal. Analysis and numerical results have been conducted to verify that the proposed scheme yields a better robustness against pointing errors than the conventional approaches.

An efficient method to measure reliability of underwater acoustic communication links

We consider the problem of evaluating the reliability of underwater acoustic communication(UWAC)systems.Reliability is a requirement for any communication system and is often defined as the probability to achieve a target bit error rate.Evaluation of system reliability is often performed empirically by conducting a large number of measurements.However,for UWAC,where experiments are expensive and time-consuming,not much data is available to perform such a reliability check.Based on the assumption that the long delay spread is the dominant characteristic of the underwater acoustic channel and for a given channel model,we offer a relaxed practical approach to evaluate the reliability of an UWAC system.As a test case,we show reliability results for the multiple input multiple output(MIMO)code division multiple access(CDMA)communication system.

Robust adaptive beamforming algorithm based on Bayesian approach

The performance of adaptive array beamform-ing algorithms substantially degrades in practice because of a slight mismatch between actual and presumed array res-ponses to the desired signal.A novel robust adaptive beam-forming algorithm based on Bayesian approach is therefore proposed.The algorithm responds to the current envi-ronment by estimating the direction of arrival(DOA)of the actual signal from observations.Computational com-plexity of the proposed algorithm can thus be reduced com-pared with other algorithms since the recursive method is used to obtain inverse matrix.In addition,it has strong robustness to the uncertainty of actual signal DOA and makes the mean output array signal-to-interference-plus-noise ratio(SINR)consistently approach the optimum.Simulation results show that the proposed algorithm is bet-ter in performance than conventional adaptive beamform-ing algorithms.