Xie Xian-zhong

An optimized vertical handoff algorithm based on Markov process in vehicle heterogeneous network

In order to solve the problem the existing vertical handoff algorithms of vehicle heterogeneous wireless network do not consider the diversification of networks status, an optimized vertical handoff algorithm based on markov process is proposed and discussed in this paper. This algorithm takes into account that the status transformation of available network will affect the quality of service (QoS) of vehicle terminals communication service. Firstly, Markov process is used to predict the transformation of wireless networks status after the decision via transition probability. Then the weights of evaluating parameters will be determined by fuzzy logic method. Finally, by comparing the total incomes of each wireless network, including handoff decision incomes, handoff execution incomes and communication service incomes after handoff, the optimal network to handoff will be selected. Simulation results show that: the algorithm proposed, compared to the existing algorithm, is able to receive a higher level of load balancing and effectively improves the average blocking rate, packet loss rate and ping-pang effect.

Interference alignment based on subspace tracking in MIMO cognitive networks with multiple primary users

The interference alignment (IA) algorithm based on FDPM subspace tracking (FDPM-ST IA) is proposed for MIMO cognitive network (CRN) with multiple primary users in this paper. The feasibility conditions of FDPM-ST IA is also got. Futherly, IA scheme of secondary network and IA scheme of primary network are given respectively without assuming a priori knowledge of interference covariance matrices. Moreover, the paper analyses the computational complexity of FDPM-ST IA. Simulation results and theoretical calculations show that the proposed algorithm can achieve higher sum rate with lower computational complexity.

Cognitive MAC protocol with minimum sampling time and cross-layer cooperation for low signal-to-noise ratio environments

The previous Decentralised Cognitive Medium Access Control (DC-MAC) protocol allows Secondary Users (SUs) to independently search for spectrum access opportunities without the need for a central coordinator. DC-MAC assumes that the detection scheme is ideal at the Physical (PHY) layer. In fact, a more complex detection algorithm is impractical in distributed spectrum sharing scenarios. Energy Detection (ED) at the PHY layer has become the most common method because of its low computational and implementation complexities. Thus, it is essential to integrate the DC-MAC with ED at the PHY layer. However, ED requires the Minimum Sampling Time (MST) duration to achieve the target detection probability in low Signal-to-Noise Ratio (SNR) environments. Otherwise, it cannot achieve the expected detection performance. In this paper, we derive an accurate expression of MST for ED in low SNR environments. Then, we propose an Optimised DC-MAC (ODC-MAC) protocol which is based on MST, and which amends the aforementioned problems of DC-MAC with ED. Moreover, the closed-form expressions for the unreliable data transmission probability are derived for both DC-MAC and ODC-MAC. We show that the simulation results agree well with the theoretical analyses. The proposed ODC-MAC can improve the data transmission reliability and enhance the throughput compared to the performance of the traditional DC-MAC.

A Time-Domain Precoder to Improve the Bandwidth Efficiency of TD-LTE Systems

This paper designs a new precoding for an OFDM system without cyclic prefix (CP), to achieve the same function with CP used in CP-OFDM system. After the analysis of CP-OFDM system, this paper constructs a modulation matrix; on this basis, introduces memory characteristics, as well as symbols feedback, and designs a time domain precoding (TDP) module. By adding the TDP module into TD-LTE link, its bit error ratio (BER) performance decreases slightly, compared to the CP system; however, due to the new system, it does not need to send CP signals; therefore, it eliminates redundancy, so the bandwidth efficiency increases.

Adaptive Network Precoding Based on SJNR to Mitigate Inter-Cell Interference

Focusing on the problem that the co-frequency interference of the downlink channels in multi-cell of multi-out multi-input (MIMO) systems, this paper used the adaptive network precoding based on the SJNR to reduce the inter-cell interference. First of all, the adaptive precoding design based on the SJNR criteria is given. In this design, each base station use independent precoding approach to suppress adjacent inter-cell interference. And then in order to decrease the handing complex by the active way, the adaptive network precoding is attained respectively in the urban and suburb area environments, two adaptive network precoding based on SJNR are obtained respectively. Simulation results show that the inter-cell interference was obviously restrained and the system performance was improved after using the active network precoding basing on the SJNR, but also reduced processing algorithms of system.

An Optimization Transmission Algorithm in MIMO Multiuser Downlinks and Application in TD-SCDMA System

This paper investigates an optimization transmission algorithm in MIMO multiuser downlinks and applies it in TD-SCDMA. A generalized optimization criterion of the JT total transmit signal and optimization of spatial characteristics of the total transmit signal in the case of the omnidirectional uniform distribution of direction of departure are introduced respectively, which can directly eliminate intersymbol interference and intracell multiple access interference. Simulation proves its performance in the TD-SCDMA system.

Power Distribution Algorithm for Multi-User Downlink of JT System

For the downlink of MIMO TDD/CDMA mobile radio systems joint transmission (JT) which has low receiver complexity is recently proposed. First investigations concerned linear transmitter algorithms and nonlinear transmitter algorithms based on the principle of THP. The nonlinear transmitter algorithms studied by M. Meurer have preferable energy efficient but restricted by coding complexity. In this paper we present a power distribution algorithm in multi-user downlink of linear JT in MIMO system (JT MIMO). First, a model of JT MIMO downlink and interference is introduced, then, we present a joint power distribution algorithm for JT MIMO downlink. By distributing the transmission power of users rationally, under achieving the SINR, minimizes the total transmitted power.