Search

The outage probability of a composite microscopic and macroscopic diversity system is evaluated over correlated shadowed fading channels. The correlations on both a microlevel and macrolevel are taken into account for the evaluations. The expression of the desired outage probability is explicitly presented, and two evaluation approaches, i.e. a compact Gaussian-Hermite quadrature method and an effective iterative algorithm, are proposed. The accuracy and efficiency of the proposed approaches are analysed, and a guideline is provided for their application. By employing the proposed evaluation approaches, results and demonstrations are presented, which display the implied effects of the corresponding parameters on the system outage performance, and reveal the potential to facilitate the design and analysis of such composite diversity systems.

Existing multi-channel Medium Access Control (MAC) protocols have been demonstrated to significantly increase wireless network performance compared to single channel MAC protocols. Traditionally, the channelization structure in IEEE 802.11 based wireless networks is pre-configured, and the entire available spectrum is divided into subchannels and equal channel widths. In contrast, this paper presents a Traffic-Aware Channelization MAC (TAC-MAC) protocol for wireless ad hoc networks, where each node is equipped with a single half duplex transceiver. TAC-MAC works in a distributed, fine-grained manner, which dynamically divides variable-width subchannels and allocates subchannel width based on the Orthogonal Frequency Division Multiplexing (OFDM) technique according to the traffic demands of nodes. Simulations show that the TAC-MAC can significantly improve network throughput and reduce packet delay compared with both fixed-width multi-channel MAC and single channel 802.11 protocols, which illustrates a new paradigm for high-efficient multi-channel MAC design in wireless ad hoc networks.

For the cases of imperfect channel state information (CSI) on the main channel in the physical-layer-security communications, we study the artificial-noise-aided robust transmit designs. We consider two optimization problems for the multi-input single-output single-antenna eavesdropper (MISOSE) and multi-input multi-output multi-antenna eavesdropper (MIMOME) systems. Under the deterministic uncertainty model (DM), the optimization problem aims to minimize the total transmit power while guaranteeing the probabilistic constraint for the signal to interference and noise ratios (SINR) at the eavesdropper, and the SINR constraint at the legitimate receiver. For the stochastic uncertainty model (SM), the optimization problem is also to minimize the total transmit power under the probabilistic constraints for the SINRs at the legitimate receiver and the eavesdropper. These problems are hard to be solved directly. We transform the optimization problems into a single-variable optimization problem with solving a sequence of semidefinite programs. By comparison, we propose another low-complexity method based on the expectation value. Finally, we verify the performance for the proposed robust transmit designs by the simulation results.

We study robust secure transmit design in terms of input covariance matrix for Gaussian multiple-input single-output (MISO) wiretap channels in the presence of a single-antenna eavesdropper. Under the assumption that the transmitter knows partial channel state information (CSI) on the main and eavesdropper's channels, we jointly design the input covariance matrices of information-bearing signal and artificial noise (AN) to maximize the secrecy rate. Unfortunately, the secrecy rate maximization (SRM) problem is difficult to solve. We derive a safe approximation to the SRM problem and propose a tractable approach to solve it. To get more insights, we discuss the rank property of the input covariance matrix of the information-bearing signal. Finally, the simulation results are provided to verify the validity and robustness of our proposed transmit design.

We investigate the outage probability for amplify-and-forward (AF) and decode-and-forward (DF) relaying in OFDM-based cooperative networks. To minimize the outage probability, the relay which has the maximum received SNR is selected as the cooperative relay. Based on the relay selection, the problems of optimal power allocation and placing relays in the optimal position are discussed. And the expressions of optimal power allocation and optimal position are finally achieved. The analysis and simulation results show that through the proposed relay selection scheme, M orders of diversity is achieved, where M is the number of potential relays. It also shows that optimal power allocation and optimal position to placing relays achieve much better performance.

The sphere decoding (SD) algorithm is widely considered to be an efficient approach to obtain maximum likelihood (ML) performance in MIMO detection. At present, almost all of the research about the SD algorithm is based on the assumption of independent and identically distributed channel coefficients. However, the channel coefficients are often correlated in practice, which cause the complexity of the SD algorithm to vary. In this paper, we give a theoretical analysis of the complexity of Fincke and Pohst's(FP) SD algorithm in spatial correlated MIMO channels; the exact expression of the expected complexity is derived. We present simulation results obtained from this expression to show the effect of spatial correlation on the complexity of the algorithm, for different Signal-to-Noise Ratios (SNR) and level of spatial correlations.

Low Earth orbit (LEO) satellite networks will work as an important component of the future telecommunications system. Multi-spot-beam antennas on satellites will allow a cellular coverage all over the Earth. However, the high speed of a mobile satellite may give rise to a large number of inter-beam and inter-satellite handovers during a call lifetime. In this paper, the author proposed a threshold-based handover prioritization (TBHP) resource management scheme for LEO satellite networks. In order to utilize the resource more effectively, the proposed method defers the channel locking time in the guaranteed handover (GH) algorithm, and in this way decreases the new call blocking probability while keeping very small forced termination probability of prioritized users. The new method is evaluated through an analytical model, from which the quantitative relation between the critical operational parameters and system performance metrics is derived. Simulation results show that our scheme offers a better chance to accept a new call while guaranteeing the handover processes for prioritized calls to a certain extent. Therefore the system resource utilization is improved.

Recently, the interpolation-based QR decomposition has been proposed in order to efficiently reduce the complexity of V-BLAST OFDM signal detection algorithm. However, it can't be directly applied to the case of different ordered matrices, which is common in most of the detection algorithms. To solve this problem, a low complexity ordering interpolation-based QR decomposition algorithm for V-BLAST OFDM systems with two transmit antennas is presented. The proposed algorithm combines the group ordering with interpolation-based QR decomposition by introducing the relationship of QR decomposition between different column ordered matrices. The algorithm can be regarded as a pre-processing method for those V-BLAST OFDM signal detection methods which apply successive interference cancellation or sphere decoding algorithm. Compared with the directly extended method of interpolation-based QR decomposition, the proposed algorithm achieves more saved cost with the increasing of the number of receive antennas, which makes it more suitable for the design of base station receivers.

In this paper, the effects of residual frequency offset on OFDM systems are analyzed, and incorrect decision will be made due to the introduced signal constellation rotation. Kobayashi and Nikitopoulos present a method of estimating the phase rotation caused by residual frequency offset. In their work, phase error is obtained by comparing signals after frequency equalization with signals after decision, then compensates the following signals by using the estimated value of the phase rotation. The method involves two decision operations and the calculation of the quantity of every signal's phase rotation, consequently its computational complexity is high. Considering that in estimation what we need is only the phase information, we propose a method which obtains the phase rotation information from data directly by using such operations as sign inversion, real and imaginary part exchanging, accumulation and avoids two decision operations. The proposed method reduce the computational complexity without degrading the performance of the original algorithm, which is more suitable for hardware implementation. Simulation results show that the degradation of SNR caused by the residual frequency offset is not more than 0.2 dB after employing the proposed algorithm on the AWGN or SUI-2 channel.

The throughput of 802.11 DCF over correlated fading channel in MANET are investigated in this paper. By obtaining the analytical representation of saturation throughput of 802.11 DCF over correlated fading channel, we get the impact of frame length and the mobile speed on throughput. Study shows the throughput decreases with the increase of mobile velocity and there exists an optimal frame length to maximize throughput under a certain velocity. Moreover, the optimal length is independent of the number of nodes.