Research On Hybrid Precoding In Massive MIMO Systems

The shortage of spectrum resources is growing in intensity,and the demand for high data transmission rates is increasing rapidly,which pose serious challenges to the current wireless mobile communication systems.Millimeter wave(mmWave)spectrum with a large amount of unlicensed spectrum resources,plays an important role in providing greater bandwidth and higher data rates.Meanwhile,due to the characteristic of extremely short wavelength,mm Wave systems are usually conjunct with massive MIMO technology,where large antenna arrays are employed to provide large array gain and increase system capacity.However,there inevitably exists path loss in mm Wave massive MIMO systems,and precoding technology has become a research hotspot to compensate it.In mmWave massive MIMO systems,the hardware complexity and cost of full-digital precoding is too high due to the large number of antennas.In addition,the traditional analog precoding cannot make full use of the spatial multiplexing gain of massive MIMO,leading to small system capacity.Therefore,hybrid precoding is adopted to overcome the drawbacks of the traditional precoding schemes.In the analog domain of hybrid precoding,thousands of phase shifters(PSs)are used,which results in considerable power loss.Therefore,this paper studies the design of hybrid precoding with low power consumption and high energy efficiency in mmWave massive MIMO systems.The main contents are as follows:Firstly,a phase modulation array(PMA)is introduced and an mmWave hybrid precoding system with low power consumption is designed.The structural characteristics of PMA are analyzed,which demonstrates the ability of equivalent amplitude and phase control.Then,a PMA-based hybrid precoding model is constructed,and the feasibility of combining PMA with mmWave massive MIMO system is illustrated by analyzing three aspects from effectiveness,power consumption and cost.On basis of which,the hybrid precoding problem is formulated.Meanwhile,it is mathematically derived that the PMA-based hybrid precoding can significantly reduce the number of radio frequency chains.To deal with the hybrid precoding problem,an enhanced orthogonal constraint algorithm and an alternating optimization algorithm are proposed,of which the complexity is analyzed.Finally,simulation results show that compared with the PS-based hybrid precoding,PMA-based hybrid precoding can reduce power loss and improve spectral efficiency.Secondly,energy efficient hybrid precoding schemes are designed by combining the switching network and PMA.Considering the flexibility of switching adaptive network,a hybrid precoding structure based on switch-phase modulation array(SPMA)is constructed,and the system model of which is described in detail.In order to design the corresponding hybrid precoding algorithm,the switching adaptive network is solved by matching theory,and then the hybrid precoding matrix is obtained.In addition,a hybrid precoding structure based on adaptive phase modulation array(APMA)is designed,and the hybrid precoding matrix is obtained by maximizing the equivalent channel gain.Simulation results show that the energy efficiency of the two proposed structures is higher than that of the existing structures.