Low-Cost Transmission Technologies For Massive Antenna Systems

Massive multiple-input multiple-output(MIMO)is one of the key technologies that ensure the performance of the new generation wireless communication system.With the increasing scale of antenna arrays,the high cost becomes an issue in the implementation of massive MIMO systems,where a sharp increase in the number of analog-to-digital converters(ADCs)leads to the high cost of hardware and power consumption.To meet the ever-growing demand for wireless communications,massive MIMO systems evolve to millimeter-wave(mm Wave)band,exploiting the rich spectrum resources in high frequency.However,the high sampling rate of wideband systems further increases the power consumption and hardware cost of ADCs.Therefore,coarse quantization by using low-resolution ADCs is an attractive approach to alleviate the problem of power consumption and hardware cost of implementing massive MIMO systems.In addition,the mm Wave wireless channel is vulnerable to the attenuation and blockages,which results in the unstable quality of service.Reconfigurable intelligent surface(RIS)is an innovative technique that provides low-cost assistance for rebuilding the wireless channel in order to improve the performance of mm Wave communications.To implement low-cost massive MIMO systems,this thesis investigates the technologies of low-resolution ADCs and RISs,which are arranged as follows:In the first chapter,the background of investigation is elaborated and the relevant researches on the low-resolution ADC and the RIS are summarized.In the second chapter,the uplink spectral efficiency of a multiuser massive MIMO system with low-resolution ADCs is analyzed in the context of orthogonal frequency division multiplexing(OFDM)under multipath fading channels.Firstly,the impact of channel power delay profile(PDP)on the variance of the quantization noise is investigated.Then,an efficient pilot scheme is developed which results in a constant average power of the quantization noise under different PDPs and also minimizes the mean squared error of channel estimation.Then,a tight approximation of the uplink achievable rate is derived in a closed form considering both the perfect channel state information(CSI)and the estimated CSI.The impact of multipath channels on the system performance is investigated.Under multipath fading channels,increasing the number of base station antennas can compensate for the rate loss due to low-resolution ADCs.Under the perfect CSI,it is found that the multipath channel with uniformly distributed power has a positive impact on the system achievable rate.For OFDM systems,the uniform multipath channel causes serious frequency-selective fading,however,it is beneficial for the coarse-quantized OFDM system.Simulations are conducted to verify these analytical results.In the third chapter,a cooperative multi-RIS assisted low-complexity transmission scheme is proposed for a mm Wave multi-antenna OFDM system.Firstly,a delay matching based scheme is put forward for simultaneously estimating the multipath channels and the transmission delays of the distributed RISs.The proposed method matches the phase of the strongest channel tap,which admits a low-complexity closed-form solution for the phase shifts of the RIS and requires limited overhead of pilots and feedback.Then,an analytical expression of the downlink achievable rate is derived.Despite the lack of independent RIS phase control for multiple subcarriers,it is proved that,by using the proposed RIS design,the downlink rate increases logarithmically with the square number of RIS reflecting elements.Two iterative optimization methods that adopt all the channel taps are also introduced for the massive antenna OFDM system,i.e.,the successive convex approximation and the manifold optimization.Numerical simulations indicate that,by using the strongest channel tap,the performance of the proposed delay matching method approaches that of the optimization methods based on all the channel taps.Meanwhile,the delay matching method has a lower computational complexity.Considering the training overhead,it is found that the proposed method can achieve a higher rate for the scenario of relatively short coherence block lengths.In the fourth chapter,a quasi-static broad coverage is designed for the RIS-assisted mm Wave massive MIMO-OFDM system by using the statistical CSI with the reduced overhead.To synthesize the power pattern reflected by the RIS,a general design method is proposed that exploits the multipath channel model and meets the customized requirement of broad coverage.For the communication of broadcast channels,the general model of multipath channel is utilized to obtain a high-rank channel matrix such that the broad coverage of the single transmit stream is generalized to the scenario of multiple streams.It is proved that,within the broad coverage,the users receive a constant average signal power.Moreover,the quasi-static broad coverage is employed for an orthogonal frequency division multiplexing access(OFDMA)system,and the analytical expression of the downlink achievable rate is derived,which is proved to increase logarithmically with the power gain of the pattern reflected by the RIS.By taking into account the overhead of pilots,the proposed quasi-static broad coverage even outperforms the design method that optimizes the phase shifts of the RIS using the instantaneous CSI.Numerical simulations are conducted to verify these observations.In the fifth chapter,the main contents of this thesis are summarized and the future research issues of the low-cost technologies in massive MIMO systems are presented.