A novel identity for the Gaussian Q-function of the sum of two non-negative variables is introduced as an extension of Craig's Q-function formula. It is shown that this new identity provides a unified framework in the performance analysis of dual-branch equal-gain combining (EGC) diversity, similar to that of Craig's Q-function formula for maximum ratio combining diversity. Then, the performance of dual correlated branch EGC in Nakagami-m fading is studied using this novel approach. For coherent modulations with error probabilities in terms of the Gaussian Q-function, it is shown that the average error probability of the dual correlated branch EGC in Nakagami-m fading is the same as the average error probability of a modeled single-channel receiver in the same fading environment. Using this fact, simple exact and approximate closed-form expressions for this average error probability are derived. The analytical results are verified and illustrated by numerical results and computer simulations.

Secrecy rate achievability in three-node amplify-and-forward cooperative systems at the presence of passive eavesdroppers without location information is statistically analyzed and optimized. First, the effective vulnerability area, the area in which no secrecy rate is achievable when an eavesdropper resides in that area, is introduced as the performance metric to measure the security of the cooperative system. Then, it is shown analytically that the best location of the relay to minimize the effective vulnerability region is on the source-destination crossing line. In addition, it is proved that the optimum relay with the best location and power allocation is located on the line segment bounded by the source and destination. Exact and some special closed-form expressions for the probability of secrecy rate achievability are obtained for the Rayleigh fading environment. Using this, the impact of the location and the relay power on the effective vulnerability area are analyzed and the best cases minimizing this area are numerically computed. It is shown that the effective vulnerability area can be reduced more than 50% in comparison with the case where no relay is used if the optimum relay location and the optimum relay power allocation are adopted.

Using the Global Positioning System (GPS) for indoor localization is challenging as the GPS signal is significantly attenuated or completely blocked by the building. In achieving indoor localization, a set of transmitters from wireless communication networks are often used as reference nodes to localize target nodes with unknown locations. The accuracy of such localization process is considerably affected by the spatial distribution of the reference nodes with respect to the target node to be localized. Hence, deploying the reference nodes at best locations will notably increase the localization precision. In this paper, a novel reference nodes deployment scheme is introduced which minimizes the average Mean Square Error (MSE) of the localization over the area of interest with certain shape. The proposed scheme is evaluated for deploying the reference nodes in the circular, square, and hexagonal localization regions. The proposed scheme is validated and illustrated by numerical simulations.

In a wireless network, while the signal attenuation due to the distance-related path loss is minimum between a node and its nearest neighbor, this is not the case for the overall attenuation when the fading effect is also taken into account. Hence, the communication best neighbor (CBN) of a node is defined as the neighbor of that node with which it has the highest channel power gain. Recently, the statistics of the physical neighborhood index of the CBN have been derived for a general fading environment in which the nodes have two-dimensional Poisson distribution. In this paper, the statistics of the distance between a node and its CBN as well as the joint CBN distance-index statistics are obtained for the same scenario. Then, the analytical expressions are specialized for the case where the communication channels follow the generalized gamma fading model. Also, the results are verified and illustrated by computer simulations and numerical results. Further, it is shown how the obtained analytical results can be used to identify the CBN more efficiently by limiting the search region and the number of neighbors that are examined.

Although cooperative relaying has been widely utilized in wireless communications, it simultaneously introduces a new source of security vulnerabilities to the wireless networks such as denial of service attacks. In order to minimize the potential security risks from relays, reliable relay authentication schemes become necessitated. In this paper, a novel relay authentication scheme is proposed to secure amplify-and-forward relay systems through utilizing the device-dependent hardware imperfection in-phase/quadrature (I/Q) imbalance. In this scheme, the I/Q imbalance associated with the receiving and transmission of the relaying process is considered as a unique device fingerprint. This fingerprint is then utilized to develop a two-parameter hypothesis testing based authentication. To enhance the performance in differentiating delicate difference between I/Q imbalances, the generalized likelihood ratio test for classical linear model is used in our hypothesis decision algorithm. The performance of the proposed authentication scheme is assessed and validated by numerical simulations. The results show significantly enhanced authentication accuracy of our new method in comparison with other I/Q imbalance based hypothesis decision algorithms.

Although cooperative relaying is generally considered as an attractive technique to improve system performances, the additional power consumption of a relaying link becomes a consistent concern. In order to characterize the power consumption of the dual-hop opportunistic relaying with power control, an exact expression for the cumulative distribution function of the total required transmission power is derived in this paper. Our analysis is based on the scenario that the best relay is selected among a set of decode-and-forward relays with homogeneous spatial Poisson distribution, such that the source-plus-relay power consumption is minimized. The required transmission power is evaluated by including the randomness of both path loss related to the locations of relays and the channel fading caused by multipath propagation. The analytical solution is verified by computer simulations and is used to compare the required power of relaying and direct links under different channel conditions. The results show that the dual-hop relaying is advantageous in long-term power saving by requiring a bounded average transmission power, while the power for the direct link communication is unbounded in some fading environments. Moreover, the required transmission power for the opportunistic relaying is less than that of the direct link with a reasonable relay density, therefore the cooperative communications can provide the power efficient transmission when the relay network is not sparse.

I/Q imbalance commonly exists in direct conversion architecture based wireless transceivers due to the mismatches of analog components between in-phase (I) and quadrature (Q) branches. In this paper, the device-dependent I/Q imbalance is utilized as transmitter fingerprint to accomplish improved wireless authentication through the collaboration of multiple receivers. In precise, two hypothesis testing based authentication methods are proposed to identify transmitter by using an I/Q imbalance related matrix. To enhance the authentication performance of these two methods, a multi-receiver collaboration scheme is proposed in our study. Simulation results validate our proposed authentication scheme and show a significant enhancement comparing to the scenario without receiver collaboration.

A new approach in fairness is proposed by using a probabilistic relay assignment strategy for cooperative communication systems. In this approach, relays are allocated to sources based on a probabilistic relay assignment function, which is characterised by the outage probability. To examine the proposed relay assignment strategy, an exact expression for the outage probability of an opportunistic coded cooperation diversity system is derived. It is assumed that the relays in this system are distributed according to a two‐dimensional homogeneous Poisson point process, and the transmission channels undergo Rayleigh fading as well as path loss. It is observed that the proposed strategy reduces the number of requests for using the relays and, thus, utilises the relays more efficiently. Furthermore, compared to the conventional opportunistic relay assignment strategy, the total power consumed by the relays decreases, while the quality of service requirements are still satisfied.

The performance of opportunistic relaying in a dual-hop amplify-and-forward relay network where the relaying nodes are distributed according to a homogeneous two-dimensional Poisson point process with fixed density is analyzed. Largely ignored in the literature, this assumption leads to more realistic results, as in a typical practical scenario neither the number of relays nor their distances from the source and destination are known. An exact expression for the outage probability of this cooperative system for general fading environments and different types of relaying is derived. The expression is then {simplified under an assumption that the radius of the relay deployment region is sufficiently large}, and specialized to additive white Gaussian noise (no fading), Rayleigh fading and severe (half-Gaussian) fading environments. Simple and tight upper and lower bounds on the outage probability are also derived. Simulation results validate the theoretical analyses and verify the accuracies of the proposed bounds.

An exact expression for the outage probability of opportunistic relaying in a dual-hop amplify-and-forward relay network is derived for general fading environments and the case where the source and destination nodes make use of directional antennas. The relaying nodes are assumed to be distributed according to a homogeneous two-dimensional Poisson point process with fixed density. This assumption is of great practical importance as in a typical practical scenario, the number of relays as well as their distances from the source and destination are random. It is observed that under some circumstances, a directional antenna at the source may permit more efficient deployment of the relay network than the case where an omnidirectional antenna is used.

A novel single-integral representation for the bivariate Rician distribution was presented in a recent letter in this Transactions (ibid., vol. 59, no. 11. pp. 2951-2954, Nov. 2011). The expression given for the bivariate Rician probability density function (PDF) [1, eq. (12a)] contains a typographical error. The correct expression for the bivariate Rician PDF is presented here.