Li Shaoqian

A Distributed Spectrum Sensing Scheme Based on Credibility and Evidence Theory in Cognitive Radio Context

Reliable detection of available spectrum is the foundation of cognitive radio technology. To improve the detection probability under sustainable false alarm rate, a distributed spectrum sensing scheme has been proposed. In this paper, we propose a new decision combination scheme, in which the credibility of local spectrum sensing is taken into account in the final decision at central access point and Dempster-Shafers evidence theory is adopted to combine different sensing decisions from each cognitive user. Simulation results show that significant improvement in detection probability as well as reduction in false alarm rate is achieved by our proposal

A new access method used in beyond 3G mobile system using MC-CDMA

A new access method that can be used in a post 3G mobile system is proposed. In the future mobile communication systems, OFDM technology probably become the main technology. On account of multi-traffic demands in the future, we should design the access method in OFDM system to accord with those demands. With this method, the system resources utilization can be optimized.

Optimal multiuser MIMO linear precoding with LMMSE receiver

The adoption of multiple antennas both at the transmitter and the receiver will explore additional spatial resources to provide substantial gain in system throughput with the spatial division multiple access (SDMA) technique. Optimal multiuser MIMO linear precoding is considered as a key issue in the area of multiuser MIMO research. The challenge in such multiuser system is designing the precoding vector to maximize the system capacity. An optimal multiuser MIMO linear precoding scheme with LMMSE detection based on particle swarm optimization is proposed in this paper. The proposed scheme aims to maximize the system capacity of multiuser MIMO system with linear precoding and linear detection. This paper explores a simplified function to solve the optimal problem. With the adoption of particle swarm optimization algorithm, the optimal linear precoding vector could be easily searched according to the simplified function. The proposed scheme provides significant performance improvement comparing to the multiuser MIMO linear precoding scheme based on channel block diagonalization method.

Multi-User MIMO Linear Precoding with Grassmannian Codebook

In this paper, multi-user MIMO (MU-MIMO) linear precoding schemes with Grassmannian codebook for downlink transmission are proposed. The proposed MU-MIMO schemes extend the point-to-point single-user Grassmannian precoding to point-to-multipoint multi-user Grassmannian precoding. We proposed two MU-MIMO schemes with the Grassmannian codebook. One scheme assumes the perfect channel information at the base station and the other scheme is under the limited feedback. These MU-MIMO linear precoding schemes with Grassmannian codebook provide significant system capacity enhancement compared with the single user MIMO (SU-MIMO) system. The results also show the performance gap between perfect channel information and limited feedback.

Performance and optimization of multistage partial parallel interference cancellation for wideband CDMA systems in multipath fading channels

In this paper, a closed-form bit error rate (BER) of hard-decision multistage partial parallel interference cancellation (PPIC) having perfect and imperfect channel estimation for complex spreading code-division multiple access (CDMA) over multipath Rayleigh channels was derived. The effects of receiving BER, power ratio of pilot to data channels, multiple-access interference (MAI) and multipath interference, additive white Gaussian noise, and other factors affecting channel estimation error are analyzed. The expression determining the optimal interference cancellation weight at path level for PPIC is first derived. Then, the oscillatory behavior of user-level-optimized PIC and the convergence of perfect channel estimation PIC and path-level-optimized PIC are validated. Results indicate that all factors determining the optimal weight certainly affect the BER performance of PPIC and that the lower BER limit of multistage PPIC depends on the adjustable factors, which include power ratio, observation length, and signal-to-noise ratio, and an unchangeable factor, i.e., number of users. In addition, the variance of MAI for complex spreading sequence is obtained, and the analytical expression can also be employed to predict the performance of multicode CDMA

The Differential Detection OFDM Cooperative Diversity System in Vehicle-to-Vehicle Communications

In this paper, we introduce the cooperative diversity (CD) into the vehicle to vehicle (V2V) communications. As the fast changes and the multi-path fading of the channel between V2V, the differential detection (DD) and OFDM (orthogonal frequency division multiplexing) is used to bypass the channel estimation and decrease the effect of the multi-path fading. As the theoretic and simulation show: The DD-OFDM-CD can improve the performance of V2V in fast changing multi-path fading channel

Analysis of the Performance of Partial Transmit Sequences with Different Subblock Partitions

This paper analyzes the performance of reducing the peak-to-average power ratio (PAPR) by partial transmit sequences (PTS) in OFDM system, and finds that it is dependent on the correlation of several candidate signals which is decided by subblock partitions and phase factors, while it is unconcerned with the input signal. The authors also prove that random subblock partition is more favorable than interleaved and adjacent subblock partitions by analysis and simulation

Cross-layer handoff management scheme in heterogeneous networks

Cross-layer handoff management aims to complete layer 3 handoff with help from layer 2. The proposed cross-layer handoff management scheme shows that cooperation between the layer 3 and layer 2 is able to improve the performance of handoff management in IP-based heterogeneous communication environment. In the next phase, cross-layer optimization for handoff management leading to a holistic connectivity management is worthy of further investigation

A Novel Method to Design Phase Factor for PTS Based on Pseudo-Random Sub-Block Partition in OFDM System

Partial transmit sequence (PTS) with pseudo-random sub-block partition can achieve lower Peak-to-Average Power Ratio (PAPR) performance. Based on the correlation of the candidate signals, we can prove that the performance is uncorrelated with the input signal. In general, the correlation of the candidate signals will increase with the number of candidate signals. As a result, the performance improvement will decrease evidently. In this paper, we provide a novel method to design the phase factor for PTS scheme, so as to achieve quasi orthogonal candidates to get better PAPR reduction performance. Simulation results prove it is more efficient than the traditional one.

Interference Avoidance Using Fractional Fourier Transform in Transform Domain Communication System

The method of fractional Fourier transform (FRFT) is introduced to transform domain communication system (TDCS) for signal transforming in the paper after theoretical analysis. The method yields optimal basis function (BF) by FRFT with optimal transform angle. The TDCS using the proposed method has wider usable spectrum, stronger robustness and better ability of anti non-stationary jamming than using usual methods, such as Fourier Transform (FT), auto regressive (AR), wavelet transform (WT), etc. The main simulation results are given as follows. First, the bit error rate (BER) Pb is close to theoretical bound of no jamming no matter in single tone or in linear chirp interference. Second, the interference-to-signal ratio (J/E) is at least 12 dB more than that of direct spread spectrum system (DSSS) under the same BER if the spectrum hopping-to-signal ratio is 1:20 in chirp plus hopping interfering. Third, the Eb/NO (when estimation difference is 90% between transmitter and receiver) is about 3.5 dB or about 0.5 dB (when estimation difference is 10% between transmitter and receiver) more than that of theoretical result when no estimation difference under Pb =102.