Junhui Zhao

Peak-to-Average Power Ratio Reduction of FBMC/OQAM Signal Using a Joint Optimization Scheme

Owing to the signal structure difference between the filter bank multicarrier with offset quadrature amplitude modulation (FBMC/OQAM) and the orthogonal frequency-division multiplexing (OFDM) systems, the existing technologies to reduce the peak-to-average power ratio (PAPR) for OFDM systems are not suitable for the FBMC/OQAM systems. This paper considers the problem of PAPR in the FBMC/OQAM systems, and to reduce the PAPR of the FBMC/OQAM signal, we propose an improved joint optimization scheme combined with the linear (i.e., partial transmit sequence (PTS)) and nonlinear (i.e., clipping and filtering (CF)) methods, named improved bilayer partial transmit sequence and iterative clipping and filtering (IBPTS-ICF) scheme. The main idea of this joint optimization scheme is clipping and filtering the processed FBMC/OQAM signal, whose probability of the peak value has been reduced by the IBPTS technique. Meanwhile, aided by the knowledge of convex optimization, the IBPTS-ICF joint optimization scheme can effectively reduce the signal distortion. The excellent PAPR reduction performance of the proposed scheme has been confirmed in our simulations.

Analysis of Channel Estimation in Large-Scale MIMO Aided OFDM Systems with Pilot Design

This paper addresses the problem of pilot contamination in multi-cell multiuser Large-Scale Multiple-Input Multiple-Output (LS-MIMO) aided orthogonal frequency division multiplexing (OFDM) systems, and the exact closed-form expression for the mean square error (MSE) of the classical least square (LS) channel estimation algorithm is derived. Then, a pilot design criterion is proposed to design the optimal pilot sequences for mitigating the pilot contamination. Following this criterion, the improved Chu sequences with perfect autocorrection property are employed. Finally, simulation results verify the effectiveness of the pilot design scheme.

Study of Connectivity Probability of Vehicle-to-Vehicle and Vehicle-to-Infrastructure Communication Systems

Considering the vehicular networks, multi-hop broadcasting is a frequently used method to deliver messages. Connectivity of wireless multi-hop networks is a critical measure for the planning, design, and evaluation of vehicular ad hoc networks. In an urban environment, vehicles can opportunistically exploit infrastructure through open Access Points (APs) and Road Side Units (RSUs) to efficiently communicate with other vehicles. Infrastructures (i.e., Base Stations (BSs), APs) are uniformly deployed along a road, while vehicles are distributed on the road randomly according to a Poisson distribution. For infrastructure-based vehicular networks, connectivity probability is the probability that an arbitrary vehicle access to the infrastructure. This paper proposes an analytical model to improve the connectivity probability of vehicle and infrastructure through multi-hop broadcasting in the infrastructure-based vehicular networks. We also consider the following factors: propagation distance, one hop transmission range, distribution of vehicles, vehicle density, average length of vehicles, and minimum safety distance between vehicles. The analytical model is validated by simulations.

Study of connectivity probability based on cluster in vehicular Ad Hoc networks

To provide a more practical analysis for performance of the VANETs (vehicular ad hoc networks), we propose a novel analysis model based on clustering. Because of the low-density deployment of the vehicles which equipped with VANET, and the effect of vehicular mobility, in the real traffic scenario, moving vehicles are divided into clusters. The proposed analysis model takes full account of the vehicles mobility and the loss of channel, then, makes contract with the classical system model, i.e., unit disk model and log-normal shadowing model. The connectivity probability of the model is studied based on cluster in two process: forwarding process and catch-up process, the two process are discussed in time slots of equal length. In this paper, some factors are also considered, such as follows: vehicle density, one hop transmission range, propagation distance, distribution of vehicles, and minimum safety distance between vehicles. The simulations validate the performance of our analytical model.

Price-Based Power Allocation in Two-Tier Spectrum Sharing Heterogeneous Cellular Networks

Attributable to the using of the same spectrum resources, heterogeneous cellular networks have serious interference problems, which greatly restricts the performance of the network. In this paper, the price-based power allocation for femtocells underlaying a macrocell heterogeneous cellular network is investigated. By exploiting interference pricing mechanism, we formulate the interference management problem as a Stackelberg game and make a joint utility optimization of macrocells and femtocells. Specially, the energy consumption of macrocell users and the transmission rate utility of femtocell users are considered in this utility optimization problem. In the game model, the macrocell base station is regarded as a leader, which coordinates the interference from femtocell users to the macrocell users by pricing the interference. On the other hand, the femtocell base stations are modelled as followers. The femtocell users obtain their power allocation by pricing. After proving the existence of the Stackelberg equilibrium, the non-uniform and uniform pricing schemes are proposed, and distributed interference pricing algorithm is proposed to address uniform interference price problem. Simulation results demonstrate that the proposed schemes are effective on interference management and power allocation.

High-speed based adaptive beamforming handover scheme in LTE-R

In recent years, high-speed railways (HSRs) are being developed rapidly all over the world because of their convenience, safety, comfort, and other advantages. However, the reliability and security of HSR wireless communication systems have faced severe challenges, such as the Doppler effect, complicated wireless channel model, frequent handovers and so on. The International Union of Railways is pushing the evolution of the global system for mobile communications for railway (GSM-R) internationally. In this study, a high-speed based adaptive beamforming handover scheme is proposed to improve the handover performance for HSR wireless communication systems. When the high-speed train enters the overlapping region, the serving evolved NodeB (eNodeB) and target eNodeB are using beamforming with different gain factors to improve the received signal quality. In addition, this scheme can dynamically adjust the handover hysteresis margins of the reference signal receiving power (RSRP) and the reference signal receiving quality (RSRQ) based on the speed and position. Simulation results have demonstrated that the proposed handover scheme can improve the handover performance by increasing the handover trigger probability and success probability effectively.

Joint Navigation and Synchronization in LEO Dual-Satellite Geolocation Systems

This paper considers the problem of tracking a mobile receiver using signals of Low Earth Orbit (LEO) satellites. Based on Time-Difference of Arrival (TDOA) and Frequency-Difference of Arrival (FDOA), we joint the time synchronization and localization together with a static reference anchor, which has unknown position. In this scenario, the satellites is asynchronous. Considering the time- and frequency- offsets as additional unknown parameters, we proposed a Maximum Likelihood estimation approach to get the reference anchors location and offsets. Then a sequential estimator jointly track the receiver location, velocity using extended Kalman filter (EKF) after revising the TDOA and FDOA measurements. Simulations demonstrate that our measurement model has a good fit, and our proposed estimator can successfully track both the receiver location, velocity with respect to the reference anchor with good accuracy.

Pilot reuse with a large number of antennas: Performance analysis and pilot contamination reduction

The performance of massive multiple-input multiple-output (MIMO) systems is heavily affected by pilot contamination. This paper considers the problem of pilot contamination in massive MIMO systems, and investigates the normalized mean square error (NMSE) of the minimum mean square error (MMSE) channel estimation algorithm in the presence of pilot contamination. An effective uplink training strategy with silent cell is proposed by carefully designing a sophisticated uplink training. Unlike many existing pilot contamination reduction schemes, the proposed scheme does not rely on the assumption of each base station needs to know the second-order statistics of either desired channels or interfering user channels. Simulation results are provided to confirm the excellent performance of this strategy.

Design of precoding matrix scheme based on maximizing frobenius norm to interference alignment

Interference alignment (IA) is a revolutionary wireless transmission strategy which can reduce the impact of interference and facilitate interference cancellation techniques. The idea of IA is to coordinate multiple transmitters so that their mutual interference can be aligned into the interference space. According to projection theory of subspace, in this paper, we propose a precoding matrix design scheme based on the maximizing Frobenius norm and use the zero-forcing (ZF) and minimum-mean-square-error (MMSE) to design the interference suppression matrix. Compared to the distributed IA algorithms and the steepest descent (SD)-based IA algorithm, simulation results demonstrate that this scheme greatly improves the channel capacity and reduces the computational complexity.

Signal path reckoning localization method in multipath environment

In the wireless localization application, multipath propagation seriously affects the localization accuracy. This paper presents two algorithms to solve the multipath problem. Firstly, we improve the Line of Possible Mobile Device (LPMD) algorithm by optimizing the utilization of the direct paths for single-bound scattering scenario. Secondly, the signal path reckoning method with the assistance of geographic information system is proposed to solve the problem of localization with multi-bound scattering paths. With the building models idealization, the proposed method refers to the idea of ray tracing and dead reckoning. According to the rule of wireless signal reflection, the signal propagation path is reckoned using the measurements of emission angle and propagation distance, and then the estimated location can be obtained. Simulation shows that the proposed method obtains better results than the existing geometric localization methods in multipath environment when the angle error is controlled.