Dongfeng Yuan

Cellular architecture and key technologies for 5G wireless communication networks

The fourth generation wireless communication systems have been deployed or are soon to be deployed in many countries. However, with an explosion of wireless mobile devices and services, there are still some challenges that cannot be accommodated even by 4G, such as the spectrum crisis and high energy consumption. Wireless system designers have been facing the continuously increasing demand for high data rates and mobility required by new wireless applications and therefore have started research on fifth generation wireless systems that are expected to be deployed beyond 2020. In this article, we propose a potential cellular architecture that separates indoor and outdoor scenarios, and discuss various promising technologies for 5G wireless communication systems, such as massive MIMO, energy-efficient communications, cognitive radio networks, and visible light communications. Future challenges facing these potential technologies are also discussed.

Cooperative MIMO Channel Modeling and Multi-Link Spatial Correlation Properties

In this paper, a novel unified channel model framework is proposed for cooperative multiple-input multiple-output (MIMO) wireless channels. The proposed model framework is generic and adaptable to multiple cooperative MIMO scenarios by simply adjusting key model parameters. Based on the proposed model framework and using a typical cooperative MIMO communication environment as an example, we derive a novel geometry-based stochastic model (GBSM) applicable to multiple wireless propagation scenarios. The proposed GBSM is the first cooperative MIMO channel model that has the ability to investigate the impact of the local scattering density (LSD) on channel characteristics. From the derived GBSM, the corresponding multi-link spatial correlation functions are derived and numerically analyzed in detail.

A Nonstationary Wideband MIMO Channel Model for High-Mobility Intelligent Transportation Systems

The recent development of high-speed trains (HSTs), as a high-mobility intelligent transportation system, and the growing demands of broad-band services for HST users, introduce new challenges to wireless communication systems for HSTs. The deployment of mobile relay stations on top of the train carriages is one of the promising solutions for HST wireless systems. For a proper design and evaluation of HST wireless communication systems, we need accurate channel models that can mimic the underlying channel characteristics for different HST scenarios. In this paper, a novel nonstationary geometry-based stochastic model (GBSM) is proposed for wideband multiple-input multiple-output HST channels in rural macrocell scenarios. The corresponding simulation model is then developed with angle parameters calculated by the modified method of equal areas. Both channel models can also be used to model nonstationary vehicle-to-infrastructure channels in vehicular communication networks. The system functions and statistical properties of the proposed channel models are investigated based on a theoretical framework that describes nonstationary channels. Numerical and simulation results demonstrate that the proposed channel models have the capability to characterize the nonstationarity of HST channels. The statistical properties of the simulation model, verified by the simulation results, can match those of the proposed theoretical GBSM. An excellent agreement is achieved between the stationary intervals of the proposed simulation model and those of relevant measurement data, demonstrating the utility of the proposed channel models.

An Improved Parameter Computation Method for a MIMO V2V Rayleigh Fading Channel Simulator Under Non-Isotropic Scattering Environments

For simulations of multiple-input multiple-output (MIMO) vehicle-to-vehicle (V2V) Rayleigh fading channels under more realistic non-isotropic scattering scenarios, we propose a new parameter computation method for the design of sum-of-sinusoids (SoS) simulation models. Compared with the existing relevant methods, the proposed method has the same simulation efficiency but provides a better approximation to the desired statistical properties of the theoretical reference model.

Energy Efficiency Analysis of Error Control Schemes in Wireless Sensor Networks

Multi-hop structure and broadcast channel of wireless sensor networks necessitate error control schemes to achieve reliable data transmission. The energy efficiency of error control schemes should be considered because of the strict energy constraints of wireless sensor networks. Wireless sensor networks require simple and facile error control schemes because of the low complexity request of sensor nodes. Automatic repeat request (ARQ) and forward error correction (FEC) are the key error control strategies in wireless sensor networks. In this paper, we discuss these error control schemes using energy efficiency analysis. We prove that energy efficiency of ARQ technique is independent of retransmission attempts and is unchangeable with the number of retransmission. The result of our analysis reveals that there is an optimum FEC scheme with the maximal energy efficiency for a target communication distance and packet size. The optimum FEC scheme is presented in this paper. In addition, ARQ is compared with FEC in terms of energy efficiency based on different communication distances and packet lengths.

Improved Artificial Fish Swarm Algorithm

Artificial Fish Swarm Algorithm (AFSA) is a novel intelligent optimization algorithm. It has many advantages, such as good robustness, global search ability, tolerance of parameter setting, and it is also proved to be insensitive to initial values. However, it has some weaknesses as low optimizing precision and low convergence speed in the later period of the optimization. In this paper, an improved AFSA (IAFSA) is proposed with global information added to the artificial fish position in updating process. The experimental results indicate that the optimization precision and the convergence speed of the proposed method are significantly improved when compared with those of original AFSA.

A Non-Stationary MIMO Channel Model for High-Speed Train Communication Systems

This paper proposes a non-stationary wideband geometry-based stochastic model (GBSM) for multiple-input multiple-output (MIMO) high-speed train (HST) channels. The proposed model has the ability to investigate the non-stationarity of HST environment caused by the high speed movement of the receiver. Based on the proposed model, the space-time-frequency (STF) correlation function (CF) and STF local scattering function (LSF) are derived for different taps. Numerical results show the non-stationarity of the proposed channel model.

Quality-of-Service Driven Power and Sub-Carrier Allocation Policy for Vehicular Communication Networks

To improve power efficiency in vehicle-to-roadside infrastructure (V2I) communication networks, this paper proposes a joint power and sub-carrier assignment policy under delay aware quality of service (QoS) requirements. Due to the real-time nature of the V2I transmissions, the proposed policy should satisfy delay aware QoS requirements with a minimized power consumption. In particular, we develop a cross-layer framework in which orthogonal frequency division multiplexing (OFDM) is employed at the physical layer and the proposed power and sub-carrier assignment policy works at the data link layer. Under the assumption that the instantaneous channel state information (CSI) of all users is known, the optimization problem can be formulated and solved with the help of a time-sharing factor. The obtained results show that both the optimal power allocation and the optimal sub-carrier assignment depend on the delay aware QoS requirements of each user. We also theoretically prove that the proposed power allocation policy converges to the classical water-filling policy if we do not consider the QoS requirements. Experimental results reveal that the proposed policy offers a superior performance over the existing resource allocation policies.

Accurate and efficient simulation of multiple uncorrelated Rayleigh fading waveforms

Simulating wideband fading channels, multiple-input multiple-output (MIMO) channels, and diversity-combined fading channels often demands the generation of multiple uncorrelated Rayleigh fading waveforms. In this letter, two appropriate parameter computation methods, namely the method of exact Doppler spread (MEDS) and Lp -norm method (LPNM), for deterministic sum-of-sinusoids (SoS) channel simulators are investigated to guarantee the uncorrelatedness between different simulated Rayleigh fading processes. Numerical and simulation results show that the resulting deterministic SoS channel simulator can accurately and efficiently reproduce all the desired statistical properties of the reference model.

Spectral efficiency analysis of mobile Femtocell based cellular systems

In this paper, we propose a new concept called mobile Femtocell (MFemtocell) network, which can be considered as a practical implementation of mobile relays (more precisely, moving networks). MFemtocells can be deployed in moving vehicles, such as trains, buses, or private cars to provide enhanced user throughput, extended coverage, and reduction of the signaling overhead and drop calls. We investigate the spectral efficiency of cellular systems with MFemtocell deployment and two resource partitioning schemes. Simulation results demonstrate that with the deployment of MFemtocells, the spectral efficiency and average user throughput can significantly be increased while the signaling overhead is reduced.