Feng Zhenming

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 new fairness criterion and its realization by using a new scheduling algorithm in the Internet

A new fairness criterion (logarithmic proportional fairness) is introduced in this paper. Under the control of this criterion, the tradeoff among fairness, network utility and total delay can be achieved in the Internet. This paper also presents a new scheduling algorithm-logarithmic proportional fair queueing scheduling algorithm (LPFQ, in short). By using this scheduling algorithm in routers, the logarithmic proportional fairness criterion and punishment to misbehaving flows can be implemented in the Internet. The theoretical analysis and simulation results prove their validity.A new fairness criterion (logarithmic proportional fairness) is introduced in this paper. Under the control of this criterion, the tradeoff among fairness, network utility and total delay can be achieved in the Internet. This paper also presents a new scheduling algorithm-logarithmic proportional fair queueing scheduling algorithm (LPFQ, in short). By using this scheduling algorithm in routers, the logarithmic proportional fairness criterion and punishment to misbehaving flows can be implemented in the Internet. The theoretical analysis and simulation results prove their validity.

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.

Power allocation between layers in multilayered space-time coding

Multilayered space-time coded modulation is an approach of combining array processing and space-time coding. Because different coded layers have different diversity gain, so unequal power levels should be allocated to the different coded layers for achieving best performance. This paper transforms the power allocation problem into two standard optimization problems. Simulation results demonstrate that new power allocation is 2/spl sim/2.5 dB better than equal power manner and 0.5/spl sim/1 dB better than experimental scheme in Tarokh et al. [May 1999].