Wei-Cheng Liu

NCTUns 4.0: An Integrated Simulation Platform for Vehicular Traffic, Communication, and Network Researches

In this paper, we present an integrated simulation platform, called NCTUns, for vehicular traffic, communication, and network researches. This platform combines the capabilities supported by a network simulator and those supported by a traffic simulator. With these simulation capabilities, NCTUns can be used to design protocols for intelligent transportation systems (ITS) communication networks such as a wireless vehicular communication network. Besides, the novel architecture of the platform enables the real-world Linux protocol stack and any real-world application to be used in simulations of such networks. In this paper, we present the design of NCTUns for supporting ITS researches and show its scalability.

Statistical Analysis of a Mobile-to-Mobile Rician Fading Channel Model

Mobile-to-mobile communication is an important application for intelligent transport systems and mobile ad hoc networks. In these systems, both the transmitter and receiver are in motion, subjecting the signals to Rician fading and different scattering effects. In this paper, we present a double-ring with a line-of-sight (LOS) component scattering model and a sum-of-sinusoids simulation method to characterize the mobile-to-mobile Rician fading channel. The developed model can facilitate the physical-layer simulation for mobile ad hoc communication systems. We also derive the autocorrelation function, level crossing rate (LCR), and average fade duration (AFD) of the mobile-to-mobile Rician fading channel and verify the accuracy by simulations.

On the performance of using multiple transmit and receive antennas in pulse-based ultrawideband systems

This paper presents an analytical expression for the signal-to-noise ratio (SNR) of the pulse position modulated (PPM) signal in an ultrawideband (UWB) channel with multiple transmit and receive antennas. A generalized fading channel model that can capture the cluster property and the highly dense multipath effect of the UWB channel is considered. Through simulations, it is demonstrated that the derived analytical model can accurately estimate the mean and variance properties of the pulse-based UWB signals in a frequency-selective fading channel. Furthermore, the authors investigate to what extent the performance of the PPM-based UWB system can be further enhanced by exploiting the advantage of multiple transmit antennas or receive antennas. Numerical results show that using multiple transmit antennas in the UWB channel can improve the system performance in the manner of reducing signal variations. However, because of already possessing rich diversity inherently in the UWB channel, using multiple transmit antennas does not provide diversity gain in the strict sense [i.e., improving the slope of bit error rate (BER) versus SNR] but can possibly reduce the required fingers of the RAKE receiver for the UWB channel. Furthermore, because multiple receive antennas can provide higher antenna array combining gain, the multiple receive antennas technique can be used to improve the coverage performance for the UWB system, which is crucial for a UWB system due to the low transmission power operation.

Cross-layer goodput analysis for rate adaptive IEEE 802.11a WLAN in the generalized Nakagami fading channel

This paper aims to evaluate the goodput performance of the IEEE 802.11 a wireless local area network (WLAN) from both the media access control (MAC) layer and physical (PHY) layer perspectives. From the physical layer perspective, we analyze the packet error rate performance of the orthogonal frequency division multiplexing (OFDM) based WLANs under the generalized Nakagami fading channel. According to the Chernoff bound analysis in the Nakagami fading channel, we derive the approximate packet error rate for the IEEE 802.11a WLAN with different data rates and fading parameters. Furthermore, we propose an efficient channel driven rate adaptation (CDRA) scheme. Through a PHY/MAC cross-layer analysis, we demonstrate that the goodput of the CDRA scheme indeed approaches to that of the optimal dynamic programming based rate adaptation method, while avoiding the complex calculations in selecting transmission parameters as the optimal method.

Joint Rate and Power Adaptation for Wireless Local Area Networks in Generalized Nakagami Fading Channels

In this paper, a channel-driven rate and power adaptation (CDRPA) algorithm is proposed for wireless local area networks (WLANs) in generalized Nakagami fading channels. Through the channel information of the first packet, the CDRPA algorithm can lower the complexity of comparing various rates and power levels. In the case of the IEEE 802.11 WLAN, the computation complexity of the CDRPA algorithms is reduced by more than 94% compared with the complete-search link adaptation. A physical and/or medium access control (MAC) cross-layer analytical model is also developed to evaluate the goodput and energy efficiency of the carrier sense multiple access with a collision avoidance MAC protocol in Nakagami fading channels. Our numerical results show that the CDRPA algorithm is not only more energy efficient in the Nakagami fading channel but can also achieve comparable and even higher throughput compared with the complete-search link adaptation approach.

Physical layer effects on the MAC goodput performance for the rate adaptive IEEE 802.11a/g WLAN

According to the IEEE 802.11n, the next generation wireless local area networks (WLAN) aim to support data rates at least 100 Mbps, as measured at the medium access control (MAC) layer. Thus, it is important to develop a cross-layer analytical model to evaluate the MAC layer goodput performance with consideration of the physical layer effects. This paper suggests such an analytical model to calculate the MAC layer goodput for the IEEE 802.11a WLAN in the Nakagami fading channel, while incorporating the effects of channel estimation, delay spread and signal detection scheme in the physical layer. Furthermore, we develop a simple and efficient channel-driven rate adaptation (CDKA) scheme to dynamically adjust the transmission parameters to maximize the MAC layer goodput. From out numerical results, we find that some physical (PHY) modes in the IEEE 802.11a are unnecessary. We also find that as rms delay spread increases, the goodput in the MAC layer can be improved due to frequency diversity. For the case of rms delay spread changing from 50 to 200 nsec with 15 dB Eh/No, the goodput is improved from 12 Mbps to 15 Mbps.

Performance Analysis of Pulse Based Ultra-Wideband Systems in the Highly Frequency Selective Fading Channel with Cluster Property

This paper presents an analytical expression for the bit error rate (BER) of the antipodal and orthogonal binary signals in the ultra-wideband (UWB) channel, of which the unique characteristics include the cluster property and highly dense multipath effect. Specifically, we consider the IEEE 802.15.3a UWB channel and take into account of the impact of all the key parameters, consisting of the cluster arrival rate, cluster decay factor, the number of rays per cluster, and the distribution of a non-Rayleigh fading signal. For the IEEE 802.15.3a UWB channel, the effects of clustering are characterized by a Poisson discrete random variable, and the magnitude of the signal is modelled by lognormal random variable. In this paper, we develop an analytical model to compute the signal with such joint continuous lognormal and discrete Poisson random variable. Hence, the developed analytical model can be useful in evaluating the performance of an UWB signal in the IEEE 802.15.3a channel without time consuming simulations

Analysis of Diversity-Multiplexing Tradeoff in a Cooperative Network Coding System

This paper addresses the analysis of diversity-multiplexing tradeoff (DMT) for a decode-and-forward (DF)-based cooperative network coding (CNC) system. The exact outage probability is also provided. Our results show that network coding can assist the relay node to improve multiplexing and diversity gain.

Bit error rate analysis in IEEE 802.15.3a UWB channels

In this paper, we present a computable bit error rate (BER) expression for the binary signals in the IEEE 802.15.3a ultra-wideband (UWB) channel. In the literature, the impacts of the RAKE receivers finger numbers and lognormal shadowing on the BER performance have not been reported yet. We propose a characteristic function (CF) based BER formula to overcome the convergence problem of the existing moment generating function (MGF) approach when the BER calculation takes account of the shadowing effect. Simulation results demonstrate that the proposed CF-based computable BER formula can accurately estimate the complete effects of the cluster and ray arrival processes, the lognormal fading as well as shadowing, and the finger numbers at RAKE receivers.

BER Analysis in A Generalized UWB Frequency Selective Fading Channel With Randomly Arriving Clusters and Rays

In this paper, we present an analytical method to evaluate the bit error rate (BER) of the ultra-wideband (UWB) system in the IEEE 802.15.4a standardized channel model. The IEEE 802.15.4a UWB channel model is more general and based on more measurements than the earlier IEEE 802.15.3a model. It also poses new challenge in analyzing UWB performance in such a channel. First, the power delay profile become a function of randomly arriving cluster and ray arrival time. Second, the signal amplitude in the IEEE 802.15.4a channel is modeled by a Nakagami random variable of which the Nakagami fading parameter is log-normally distributed. Thus, the signal amplitude is a nonlinear function of a log-normally distributed random variable. By means of counting integral of Lebesgue measure theory, the analytical expression for the BER performance in the IEEE 802.15.4a UWB channel is presented. We apply this analytical model to investigate the impacts of various UWB channel parameters on the system performance and provide some useful insights into the design of UWB transceiver.