Yin Changchuan

An improved carrier frequency synchronization algorithm with spatial diversity in MIMO-OFDM system

Carrier frequency synchronization is important in MIMO-OFDM systems. Any carrier frequency offset will cause a loss of subcarrier orthogonality which results in ICI and hence performance degrades severely. In this paper, a preamble structure for MIMO-OFDM systems is proposed. Based on the structure, the carrier frequency synchronization algorithm in burst data transmission for MIMO-OFDM systems is improved. The paper investigates the value of the improved algorithm with transmit and receive diversities for carrier synchronization in MIMO-OFDM systems. The simulation results show that the carrier synchronization performance in MIMO-OFDM systems with the improved algorithm exploiting transmit and receive diversity is efficient and robust, especially in low signal-to-noise ratio condition.

AP load balance based handover in software defined WiFi systems

In existing wireless systems its hard for an operator to change the network strategy under heavy load due to its proprietary and inflexible hardware based architectures. This paper explores the concept of software defined networking (SDN) in wireless networks. An access point (AP) load balance based handover scheme in SDN WiFi systems is proposed for overlapping wireless local area network cells to take efficient handover based on AP load. We implemented the proposed load balancing handover scheme in Mininet-WiFi emulator which could handle the APs from a centralized controller and help the test client determine how and when to connect with the right AP and take efficient handover based on AP load. New interface is added with the station, clients traffic is tested at different positions and improved throughput for mobile clients is obtained. Experimental results show that total network throughput is enhanced after a successful handover.

Non-orthogonal pilot pattern for sparse channel estimation in large-scale MIMO-OFDM system

Abstract From the perspective of compressed sensing (CS) theory, the channel estimation problem in large-scale multiple input multiple output (MIMO)-orthogonal frequency division multiplexing (OFDM) system is investigated. According to the theory, the smaller mutual coherence the reconstruction matrix has, the higher success probability the estimation can obtain. Aiming to design a pilot that can make the system reconstruction matrix having the smallest mutual coherence, this paper proposes a low complexity joint algorithm and obtains a kind of non-orthogonal pilot pattern. Simulation results show that compared with the conventional orthogonal pilot pattern, applying the proposed pattern in the CS channel estimation can obtain the better normalized mean square error performance. Moreover, the bit error rate performance of the large-scale MIMO-OFDM system is also improved.

A solution to the upper and lower bound of outage probability in ad hoc networks

In this paper, an easy solution to the upper and lower bound of the outage probability in ad hoc networks is presented. First we calculate the characteristic function of a model under power control. Then, we introduce some existing results under a special model which we call it the system model. By comparing the characteristic functions of the normalized interference under two models, we find that under the system model, if we change the node density λ into other parameters in the expression of the bounds, upper and lower bounds of other models (such as a model employing channel inversion as the power control strategy) can be obtained. This method is proved to be correct by comparing our results with the existing ones, and simple in the calculation.