Researches On Key Technologies Of Dual- Polarized Antenna Receiver In High-capacity Microwave Communication

With the development of wireless communication networks and the emergence of new smart mobile terminals,people have greater demands for higher transmission speed,higher audio quality and more diverse data services.Thus microwave backhaul links face high capacity challenge.In order to meet the requirement of the reliable transmission of high-speed data,the existing microwave communication system adopts many technologies to improve the capacity such as high-order 4096-QAM modulation,low roll-off factor,112 MHz large bandwidth,cross-polarization interference canceller(XPIC),line-of-sight multiple-input multiple-output(Lo S-MIMO),dual-polarized antenna.These technologies support the single-carrier microwave communications with 112 MHz bandwidth to enable the information transmission rate up to 2 gigabits per second(Gbps).However,high-order QAM modulation and low roll-off factor could result in a reduced Euclidean distance between adjacent constellation points,which are greatly sensitive to timing offset and cross polarization interference.Therefore,this paper investigates the key technologies of dualpolarized antenna receiver in high-capacity microwave communication,which includes the symbol timing recovery(STR)and XPIC technologies.The detailed research results are as follows:1)A pre-filter assisted STR algorithm and a dual-polarization antenna multiplexing STR schemes are proposed: a)The conventional STR algorithm is difficult to make 4096-QAM modulated signal converged.To solve this problem;a pre-filter is designed in conventional STR loop.b)The existing microwave communication dual-polarization antenna receiver adopts two timing recovery loops to handle two polarization signals respectively,which wastes the hardware resources.Therefore,a dual-polarization antenna multiplexing STR scheme is proposed.In this scheme,two polarization signals are recovered via multiplexing a STR loop,which reduces complexity of implementation.According to the simulation results,the convergence speed and BER performance of the proposed scheme are almost with no degradation compared with the original recovery scheme.2)A cross polarization interference cancellation adaptive algorithm that decreases the computational complexity of the traditional neighborhood-assisted symbol-based decision(N-SBD)algorithm is proposed: The update equation in the traditional N-SBD algorithm needs a large number of exponential and multiplication operations,which increases the complexity of calculation and hardware implementation.Based on the simplified calculation of the error function,a simplified N-SBD algorithm is proposed.The proposed algorithm utilizes the equidistant relationship of the constellation points in the adjacent region,simplifies the similar error items and uses the step function to approximate the exponential weighting factor,which avoids the complex operations in the N-SBD algorithm and greatly reduces the complexity of computation and hardware implementation.The simulation results show that the convergence speed,the residual steady-state error after convergence,and the BER performance of the proposed algorithm,under the same conditions,are close to the NSBD algorithm.3)Combining the generalized multilevel modulus algorithm(GMMA)with XPIC: Initially,the GMMA is utilized for single-antenna adaptive blind equalization,which converges the received signal to multiple modulus.The outstanding advantage of the GMMA algorithm is that more modulus values participate in the error update,making the cost function more consistent with the constellation diagram.This paper combines GMMA with XPIC for crosspolarization interference cancellation in 4096-QAM modulation.