Research On Hybrid Carrier System Order Selection And Non-Orthogonal Multiple Access Based On Power-Domain

From the history of the development of communication,it can be seen that the modern mobile communication has technological innovation every ten years,and the system performance can be improved significantly every time.Now,the fifth generation(5G)and future mobile communication have received considerable attention from academia and industry.Many typical scenarios of the future mobile communication have critical requirements,including high spectral efficiency,large device density,and high reliability.Facing performance requirements of the future communication system,this thesis studies the order selection strategy and non-orthogonal multiple access(NOMA)based on power domain to improve the transmission reliability and the spectral efficiency.For merging advantages of single carrier-frequency division multiplexing access(SC-FDMA)and orthogonal frequency division multiplexing access(OFDMA),a hybrid carrier(HC)system based on weighted fractional Fourier transform(WFRFT)was proposed.This system can change from the SC-FDMA system to the OFDMA system by controlling the WFRFT order.HC signal energy has an even and symmetrical energy distribution in the time-frequency domain,and WFRFT can also average channel interference in the time-frequency domain at the receiver.Based on the above advantages,related research has proven that HC systems can obtain better bit error rate(BER)performance than SC-FDMA and OFDMA systems.However,research on HC systems is still in the early stages.Therefore,this thesis will study HC signal distribution characteristics and the HC system order selection strategy.The existing literature on HC signal characteristics is all based on simulation results and is lack of theoretical analysis.This thesis firstly analyzes baseband HC signal real and imaginary parts probability density function(PDF),and the accurate and rigorously established closed-form expression of PDF is derived.It is verified that this PDF expression can describe HC signal probabilistic nature accurately by simulation results.The HC signal PDF can be used to analyze NOMA inter-user interference(IUI)and deduce NOMA user BER expressions.Based on the theoretical analysis of PDF,this thesis further studies the HC signal peak-to-average power ratio(PAPR)and obtains the analytical expression of the complementary cumulative distribution function(CCDF)of PAPR.For describing oversampled HC signal PAPR,this thesis proposes to use the adjustment parameter to modify the CCDF analytical expression.Finally,the derived analytical expression can accurately describe the original and oversampled HC signal PAPR characteristics.Through analyzing HC signal PAPR,it can be concluded that HC signal PAPR is controllable,which can be used as a reference for the proposed order selection strategy.Considering the controllable PAPR of HC signals and the uplink power control(UPC),this thesis proposes a new order selection strategy for the uplink HC system to enhance the BER performance.When the UPC parameter is known,this thesis also builds a relationship between the HC system order selection and the distance of the user equipment(UE)and the base station(BS).Through simulations,the HC system with the proposed order selection strategy is verified to obtain better BER performance than the single conventional SC-FDMA or OFDMA system.Based on the order selection strategy,this thesis also proposes a constellation and order selection model,which can balance the spectral efficiency and the cell coverage.This model can guarantee the transmission reliability of the far UE when expanding the cell coverage.Nevertheless,for improving the system spectral efficiency and user connections,a new multiple access technique should be introduced in HC systems.At the moment,NOMA is a promising technique of 5G multiple access candidates.This thesis proposes utilizing NOMA in HC systems to improve the system spectral efficiency and user connections,which is called NOMA-HC system,and investigates the optimal order selection to obtain the maximum sum spectral efficiency.In the practical system,NOMA cannot avoid IUI and error propagation because of the actual error decoding in the successive interference cancellation(SIC)process.Therefore,the optimal UE order selection to maximize the two-user sum spectral efficiency in the uplink is formulated by analyzing IUI and error propagation,and the optimal solution is obtained.In the uplink,UEs are geographically distributed in the cell,and the transmission environment is dynamic.Therefore,imperfect synchronism possibly happens in the uplink NOMA transmission.This thesis proposes a decoding scheme for the imperfect synchronized uplink NOMA-HC system to improve BER performance.This decoding scheme uses the cyclic prefix(CP)to mitigate imperfect synchronism effects and utilizes the SIC-phase compensation(SIC-PC)technique to improve NOMA user BER performance.Compared with other existing decoding schemes,the proposed decoding scheme can improve imperfect synchronized NOMA user BER performance substantially.