ABSTRACT As the volume of multimedia data exchanged over the Internet continues to grow, the problem of preventing the unauthorized duplication of copyright‐protected images or the dissemination of undesirable material such as pornographic pictures has become increasingly important. The majority of the images circulated over the Internet are coded in the JPEG format. Thus, the present study proposes a novel digital feature retrieval scheme designed to detect unlawful dissemination of pre‐selected JPEG images. In the proposed approach, the packet‐level features of the target JPEG image are collected in advance and are stored in a feature database. Thereafter, the features of all the packets passing through a nominated router are compared on‐the‐fly with those in the feature database in order to detect any transmissions of the target images. The experimental results show that the proposed packet‐level forensic scheme is far more efficient than existing application‐level schemes. As a result, the proposed scheme provides a viable solution for the background monitoring of JPEG streams over large‐scale network environments such as the Internet in order to detect unlawful transmissions and to compile digital evidence of such transmissions for possible future legal proceedings. Copyright © 2012 John Wiley & Sons, Ltd.

This paper is divided into two parts. In the first part, we analyze outage probability of dynamic decode and forward (DDF) with network coding (NC) and compare outage probability with using NC and without using NC. In the second part, we use MATLAB programming language to simulate our system model. We simulate outage probability and compare the simulation result with numerical value of outage probability in the first part to prove the correctness of the analytical outage probability. Our results show that network coding can improve the outage probability of considered system model.

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.

Abstract—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 receiver’s 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. Index Terms—Bit error rate (BER), IEEE 802.15.3a channel model, RAKE receiver, shadowing, ultra-wideband (UWB). I.

In this paper, we propose a novel target selection algorithm to reduce handoff frequency in wireless multi-hop relay networks. In a metropolitan environment, signals are reflected and shadowed by buildings. Thus the signal changes rapidly. To mend this problem, IEEE 802.16j defines a new network component-relay station (RS) to improve coverage. Since an RS looks like a base station (BS) for MS, handoff frequency increases proportionally to the number of deployed RSs. Signaling overhead and interruption in upper layer application service become serious problems. The proposed target selection algorithm combining signal strength and time-of-arrival information of frame can reduce handoff frequency significantly.

In this paper, we present bit error rate (BER)- minimized space-time-frequency (STF) block codes for multi- input multi-output (MIMO) highly frequency-selective block- fading channels. We consider the IEEE 802.15.3 a ultra-wide band (UWB) channel models (CM) 1-4. Based on a new STF block codes design criterion with the objective of minimizing BER, we develop an efficient searching algorithm for the design of the optimal STF block codes which maximize the coding gain. For 128 subcarriers with two subcarriers jointly encoding with 2-4 transmitting antennas, we find that the optimal STF block codes for all the IEEE 802.15.3 a UWB channel models CM 1-4 can be found. Furthermore, the designed STF block codes outperform the recently published high-rate full-diversity STF codes [1] by 1 dB. Last, the proposed STF codes can be decoded by maximum likelihood decoding approach, which is simpler than the sphere decoding principle used in [1].

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.

This paper provides the bit error rate (BER) analysis of the antipodal and orthogonal binary signals under the ultra-wideband (UWB) channel. We offer an analytical expression and its evaluation formula for the BER. The channel model we consider is the IEEE 802.15.4a UWB channel. We take into account of the impact of all the key parameters, including inter-cluster arrival rate, cluster decay constant, the inter-ray arrival rate, ray decay constant, parameters of the power delay profile (PDP), and the distribution of a Nakagami fading signal. For the IEEE 802.15.4a UWB channel, the effects of clustering are characterized by a Poisson process, and the inter-ray arrival time is modeled as the hyperexponential random variable. We propose a systematic analytical method to evaluate the BER performance of the UWB signal associated with such joint continuous Nakagami and discrete Poisson random variable. Thus, the developed analytical model is useful in evaluating the performance of an UWB signal in the IEEE 802.15.4a channel without time consuming simulations.

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.

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.

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.

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.