Lu Mingquan

Asymmetric hexagonal QAM based OFDM system

OFDM (orthogonal frequency division multiplexing) has been widely used in wire and wireless communications, because of its efficient use of the frequency spectrum and good multi-path tolerance. However, the OFDM system is very sensitive to frequency offset and phase noise. In order to overcome this disadvantage, asymmetric hexagonal QAM is presented in this paper as a new modulation method to solve this problem. Without weakening the resistance to noise, an asymmetric hexagonal QAM based OFDM system is easy to get the sub-carrier frequency and it is more convenient for its synchronization. In this paper, the asymmetric hexagonal QAM based OFDM system is designed and simulated by SystemView. Then the simulation results are presented and analyzed; the properties of asymmetric hexagonal QAM and rectangular QAM are compared.

Optimal wavelet packet based multicarrier modulation over multipath wireless channels

Multicarrier modulation is a popular technique for wide band communications; over wireless channels, which divides the channel into orthogonal and overlapping subchannels. The main purpose of this paper is to replace the conventional FFT based multicarrier modulation with orthogonal wavelet packet in order to get a more flexible and robust performance. Furthermore, the wavelet packets are optimized in the sense of minimizing the power of intersymbol interference (ISI) and intercarrier interference (ICI). The performance of the optimal wavelet packet based multicarrier modulation system is simulated and compared with the conventional wavelet and FFT based multicarrier modulation systems.

A model based on congestion pricing for QoS

Fairness of resource allocation scheme is very important for realizing quality of service (QoS) in Internet. However, the current scheme implementing TCP protocol is unfair for the users with different round trip times (RTTs). In this paper; we introduce a new model based on dynamic congestion price that can guarantee fairness of allocating resource between users with different RTTs. Thereby, the scheme on this model can provide differential services easily.