Weiling Wu

Different behavioral characteristics of Web traffic between wireless and wire IP network

Web service has become the largest consumer of Internet resources and is a promising 3G wireless service. Constructing an accurate model of Web traffic is essential for networking experiments involving end-to-end performance. In this paper, we employ an approach of analyzing TCP/IP header to obtain Web traffic model. By comparing Web traffic of wireless and wire network, we present some different characteristics between them that reflect the influences of wireless limited bandwidth and high tariff. Furthermore, Hurst parameter shows that the self-similar nature of wireless Web traffic still exists.

Channel estimation based on pilot subcarrier in space-time block coded OFDM system

This paper describes an efficient channel estimation technique for space-time coded (STBC) OFDM systems based on comb-type pilot. The STBC is used in frequency domain to obtain the orthogonal channel estimations from the different transmission antenna with specific pilot pattern in FFT grid. With the assumption of the same of consecutive subcarriers channel impulse responses in frequency domain for the case with a very small ratio of channel delay spread to OFDM symbol interval, the channel state information at pilot subcarriers is easy to be obtained according to lease square (LS) criteria, also the complexity of this system is reduced, while the channel interpolation using linear and spline cubic interpolation. At last a simulation result is given to show this system a good performance in multipath fading channel based on Jakes model.

DCT-Based Channel Estimation Method for MIMO-OFDM Systems

This paper presents two discrete cosine transform (DCT)-based pilot-symbol-aided channel estimation methods using different pilot arrangement schemes. By exploiting the properties of DCT, both proposed methods mitigate the aliasing effect introduced in discrete Fourier transform (DFT)-based channel estimation method when the multi-path fading channels have non-sample-spaced path delays. Of these two DCT-based channel estimation methods, one reduces the additive white Gaussian noise (AWGN) and inter-carrier interference (ICI) significantly by iteration, while with reasonable constraint and phase shifted pilot sequences for each transmitter antenna, the other one can achieve highly efficient and accurate estimation without sacrificing much system overhead. The computer simulation results demonstrate effectiveness of the proposed DCT-based channel estimation methods.

A New Extended rtPS Scheduling Mechanism Based on Multi-Polling for VoIP Service in IEEE 802.16e System

Making full of multi-polling technique and the silence characteristic of VoIP service, a new Extended rtPS uplink scheduling algorithm is proposed based on IEEE 802.16e system. Via analysis of theory and simulation, the proposed algorithm has superior performance in view of throughput and capacity at the same time it hsa little influence in the delay requirement of VoIP service.

Performance analysis of MMSE multiuser detection

Performance analysis of minimum mean-squared error (MMSE) multiuser detection over a synchronous multipath channel is considered in this paper. Assuming the channel parameters are known, analysis shows that both the signal-to-noise ratio at the output of the MMSE detector and near-far resistance are related to the cross-correlation matrix of the combined spreading waveforms. Computation results demonstrate that the MMSE detector can achieve good performance under severe conditions, including large number of users and large channel length.

The performance analysis of a receiver with combining multistage parallel interference cancellation and antenna array

This paper gives a new CDMA receiver combining multistage parallel interference cancellation that is one of multiuser detection methods and antenna array. The linear parallel interference cancellation (PIC) scheme is described using matrix algebra, so it is combined with multiple antennas as a linear space-time detector. This receiver is based on minimizing the mean-squared error (MMSE) criteria to get all user data. The weights for the receiver structure can be found by the steepest descent method that is a novel trained adaptive algorithms, then used to combine the soft-decision output user data after antenna array and multistage parallel interference cancellation processing. At last, the computer simulation result is given, shows good performance of this receiver to resist multipath effect.

Monte Carlo Probabilistic Data Association Detector for SFBC-VBLAST-OFDM System

In this paper, we propose a spatial multiplexing and diversity joint transmit structure for MIMO-OFDM system where space-frequency block coding (SFBC) is used over all spatial multiplexing layers to obtain both space diversity and frequency diversity gain. We have derived a Monte Carlo probabilistic data association (PDA) detector to get a better bit error rate (BER) performance compared to generic PDA detector. Computer simulation results show that the proposed detector can reduce the intersymbol interference (ISI) greatly, and improve the system performance significantly while the computation complexity has been lower to a proper lever.

A novel time-difference-of-arrival estimating approach based on FWT

This paper investigates the relationship between fast Walsh transform (FWT) and the autocorrelation of m-sequence. On this basis a novel approach to estimate the time-difference-of-arrival (TDOA) that benefits from binary tree searching is proposed. Computer simulation indicates that this method is much more effective than the conventional ones with enough reliability.

A model of mobile satellite channel

The signal propagation character in a communication channel is the base of communication system design. The factors that affect the signal in the mobile satellite channel are analyzed here and a new channel model is presented. The new model is based on layered Markov chain, and most of the factors affecting the communication signal are included in it, but the model is also easy to use in communication design. Simulation proves that the model is usable.

Improved design criterion for good space-time trellis-codes under block fading channels

The design criteria for space-time codes under block fading channels are the rank criterion and the determinant criterion, which are widely cited in the literature. These criteria are not very tight under some circumstances. In this letter, we derive a tighter design criterion for space-time codes. Based on our criterion, we have found good space-time codes by computer search. The complexity of systematic search for good space-time codes is a big obstacle to get good codes. Using our new design criterion, the complexity of search is dropped down dramatically. Simulations show that our new codes have superior performance over the existing codes.