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This paper studies the achievable secrecy performance of multiple-input multiple-output wiretap channels in the presence of imperfect channel state information (CSI) with practical low-complexity transmission schemes. In particular, we propose a general order transmit antenna selection and power-efficient output-threshold maximal ratio combining scheme. Two separate cases depending on the availability of the eavesdropper’s CSI at the transmitter are considered. New closed-form expressions of the secrecy outage probability and the average secrecy rate are obtained. In addition, the secrecy diversity order and array gains, high signal-to-noise ratio slope, and power offset are characterized through asymptotic analysis, which enables the characterization of the effect of imprecise transmit antenna selection, output-threshold, and imperfect CSI on the secrecy performance. Numerical results are presented to validate the main outcomes of this paper. [ABSTRACT FROM PUBLISHER]

In this paper, we provide a comprehensive analytical framework on the performance of multiple-input multiple-output (MIMO) mutlihop amplify-and-forward relay network employing transmit antenna selection (TAS) with receive maximal ratio combining (MRC) in the presence of randomly located interferers. The channel fading models per hop are assumed to be independent and follow exponential random distribution, and the interference is distributed according to the spatial Poisson point process PPP, which is further known as symmetric alpha stable distribution. The impact of spatial dependence across multiple antennas is facilitated by considering three different network interference models: 1) the isotropic model, where all receive antennas see interference belonging to the same Poisson point process (PPP); 2) the independent model, where each receive antenna sees interference belonging to a different independent PPP; and 3) the mixture model, where each receive antenna sees the superposition of the two previous models. The end-to-end transmission is performed using two TAS modes, which includes signal-to-noise ratio (SNR)-based selection, and signal-to-interference noise ratio (SINR)-based selection. The analysis provides new analytical results for the outage probability and symbol error rates (SER). In addition, the impact of feedback delay on the performance of the proposed system for SNR-based selection is investigated. We further study the optimum resource allocation strategies including power allocation, position allocation, and joint allocation for power and position. The obtained results are clarified through selected numerical and simulated examples. [ABSTRACT FROM AUTHOR]

In this paper, we present a comprehensive investigation on the secrecy performance of opportunistic relay selection systems employing the decode-and-forward protocol over Rayleigh fading channels. Considering a practical setting where direct link between the source node (Alice) and the destination node (Bob) is available, we study the secrecy performance of three different diversity combining schemes, namely, maximum ratio combining (MRC), distributed selection combining (DSC), and distributed switch-and-stay combining (DSSC). Throughout the analysis, we consider two different scenarios based on the availability of the eavesdropper's channel state information (CSI), i.e., Scenario A, where the eavesdropper's CSI is not available at Alice and the relay, and Scenario B, where Alice and the relay have knowledge about the eavesdropper's CSI. For Scenario A, we derive exact closed-form expressions for secrecy outage probability and simple asymptotic approximations for the secrecy outage probability, which enable the characterization of the achievable secrecy diversity order and coding gains. For Scenario B, we derive closed-form expressions for the achievable secrecy rates. For both scenarios, we investigate the impact of feedback delay (outdated CSI) on the secrecy performance wherein exact and asymptotic secrecy outage probability and closed-form expressions of the secrecy achievable rates are obtained. Our analytical findings suggest that both the MRC and DSC schemes achieve the maximum diversity order of $K+1$ where $K$ is the number of relays. In addition, the feedback delay has a significant impact on the achievable secrecy performance by reducing the achievable diversity order to two. [ABSTRACT FROM PUBLISHER]

In this paper, we propose transmit antenna selection with maximal ratio combining (TAS/MRC) in dual-hop decode-and-forward spectrum-sharing relaying networks with the primary user's interference and outdated channel state information (CSI). In this network, a single antenna that maximizes the received SNR is selected at the secondary transmitter, and the MRC is adopted at the secondary receiver. To efficiently evaluate the impact of key parameters on the system performance, we derive the exact analytical expression for the outage probability of the secondary network in a Rayleigh fading channel. Moreover, we present simple asymptotic expressions for the outage probability in a high SNR regime, which reveal practical insights on the achievable diversity order and coding gain. The findings suggest that whether the outdated CSI concerning the secondary transmission links has significant impact on the outage probability of the system depends on the interference power constraint at primary receivers. Specifically, under the proportional interference power constraint, the achievable diversity order is affected by imperfect CSI regarding the secondary transmission links, and the diversity–multiplexing tradeoff is independent of the primary network. However, under the fixed interference power constraint, the error floor is displayed, and the achievable diversity order reduces to zero regardless of the CSI concerning the secondary transmission links. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a new differentiated successive-interference cancellation (DiffSIC) ordering technique for uplink multiple-user systems. Unlike classical successive-interference cancellation (SIC), DiffSIC is capable of differentiating users according to their priority or class of service by selecting a detection order that best fits the users' service profiles. In addition, DiffSIC is able to achieve the optimal SIC detection order that results in the best overall system performance. To develop DiffSIC, we introduce analytical methods toward finding instantaneous symbol error rates (SERs) for zero-forcing SIC (ZF-SIC) and minimum mean square error SIC (MMSE-SIC) detectors. Furthermore, we devise two procedures to reduce the computational complexity associated with the computation of SER and the enumeration of detection orders. We present a number of numerical results that clearly demonstrate the ability of DiffSIC to accomplish service differentiation and overall performance improvement in general. [ABSTRACT FROM AUTHOR]

The IEEE 802.16 wireless metropolitan area network (WMAN) standard is a promising and cost-effective, last-mile wireless technology for the provision of broadband Internet access to end users. In this paper, we present an accurate analytical model that describes the contention-based bandwidth (BW) request scheme of the 802.16 standard, which is also known as WiMAX, for the persistent and nonpersistent request generation cases. We first model the contention procedure with a Markov chain, taking into account the exponential back-off procedure as well as the waiting time for a BW assignment and the possible timeout for lost messages. The accuracy of the model is then evaluated by comparing it with simulation results for a wide range of values of the parameters involved. We use this model to accurately calculate the capacity of the contention slots in delivering BW requests, from which the average access delay is also found. These measures are used to determine a proper configuration tor the efficient operation of the contention-based BW request scheme. The proposed model provides a useful analytical tool for devising adaptive configuration mechanisms for the contention access mode of the 802.16 medium access control (MAC) layer. [ABSTRACT FROM AUTHOR]

In this paper, we propose a cross-layer optimization scheme for delivery of scalable video over multirate wireless net- works, in particular the popular 802.11 based wireless local area network (WLAN). The 802.11 based networks use a link adaptation mechanism in the physical layer (PHY) to maintain the reliability of transmission under varying channel conditions. When channel condition worsens, the reliability is maintained by employing more robust modulation and coding schemes, at the cost of reduced PHY bit rate. The reduced bit rate will result in lower available throughput for applications. For scalable video streaming applications, the conventional solution to this problem is to reduce the video bit rate by dropping the higher enhancement layers of the scalable video. We show in this article that the video quality can be improved, if the link adaptation scheme uses more intelligent reliability criteria and adjusts the PHY parameters used for delivering each video layer, according to the relative importance of that layer. Our scheme achieves better video quality without increasing the traffic load of the WLAN. For this purpose we present temporal fairness constraints and formulate an optimization problem for assigning different PHY modes to different layers of scalable video; the solution to this problem provides a set of PHY configuration parameters that achieve the highest possible video quality while meeting the admission control constraints in the network. Performance evaluations demonstrate that our method outperforms the existing mechanisms. [ABSTRACT FROM AUTHOR]

The prevalent use of best-effort topology- driven IP routing protocols with shortest path calculations can often lead to serious imbalance of packet traffic distribution when least cost paths converge on the same set of links, leading to unacceptable delays or packet loss even in the presence of feasible paths over less utilized links. Recently proposed enhancements to common routing protocols are promising to overcome such shortcomings by providing the means to distribute link state information that is more pertinent to traffic engineering in routed networks. This article presents several key results on the performance of the recently proposed OSPF-TE, with particular emphasis on OSPF- It protocol traffic overhead and the impact of new link state advertisement triggering mechanisms on traffic-engineered routing accuracy. [ABSTRACT FROM AUTHOR]

Presents a novel recursive algorithm for generating higher order multidimensional discrete cosine transform (DCT). Importance of DCT in video processing applications; Scalable parallel architectures for computing the transform; Two-dimensional recursive architectures for the DCT; Conventional row-column decomposition.