Aydin Behnad

Analysis of Outage Probability and Throughput for Half-Duplex Hybrid-ARQ Relay Channels

We consider a half-duplex wireless relay network with hybrid-automatic retransmission request (HARQ) and Rayleigh fading channels. In this paper, we analyze the average throughput and outage probability of the multirelay delay-limited (DL) HARQ system with an opportunistic relaying scheme in decode-and-forward (DF) mode, in which the best relay is selected to transmit the sources regenerated signal. A simple and distributed relay selection strategy is considered for multirelay HARQ channels. Then, we utilize the nonorthogonal cooperative transmission between the source and selected relay for retransmission of source data toward the destination, if needed, using space-time codes. We analyze the performance of the system. We first derive the cumulative density function (cdf) and probability density function (pdf) of the selected relay HARQ channels. Then, the cdf and pdf are used to determine the exact outage probability in the lth round of HARQ. The outage probability is required to compute the throughput-delay performance of this half-duplex opportunistic relaying protocol. The packet delay constraint is represented by L, which is the maximum number of HARQ rounds. An outage is declared if the packet is unsuccessful after L HARQ rounds. Furthermore, simple closed-form upper bounds on outage probability are derived. Based on the derived upper bound expressions, it is shown that the proposed schemes achieve the full spatial diversity order of N + 1, where N is the number of potential relays. Our analytical results are confirmed by simulation results. In addition, simulation shows that our proposed scheme can achieve higher average throughput, compared with direct transmission and conventional two-phase relay networks.

Performance Analysis of Opportunistic Relaying in a Poisson Field of Amplify-and-Forward Relays

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.

Multi-Hop Amplify-and-Forward Relaying on Nakagami-0.5 Fading Channels

The performance analysis of a wireless communication system on Nakagami-0.5 fading channels has importance, as it evaluates the system in a worst case scenario. This analysis becomes more crucial when a high level of quality of service is required. The performance of a multi-hop amplify-and-forward relaying system on Nakagami-0.5 channels is considered. First, it is shown that the harmonic mean of independent gamma random variables with shape parameter 0.5 has again gamma distribution with the same shape parameter. Then, using this fact, closed-form expressions giving accurate approximations for the outage probability, the average symbol error probability, and the ergodic capacity of the multi-hop relaying system are derived. The analytical results are verified by simulations.

Probability of Node to Base Station Connectivity in One-Dimensional Ad Hoc Networks

In this letter, probability of node to base station connectivity in a one-dimensional ad hoc network is calculated. It is assumed that the location of the nodes follows a homogeneous Poisson point process, while the base stations are either another independent Poisson point process or with regular deployment. Nodes are connected to the base stations directly or in multi-hop fashion using other nodes. Analytical formulas are obtained and compared by numerical results and simulations.

Upper bound for the performance metrics of amplify-and-forward cooperative networks based on harmonic mean approximation

In many studies of amplify-and-forward cooperative networks, a harmonic mean approximation has been used for the instantaneous signal-to-noise ratio of each dual hop relaying branch. This approximation overestimates the signal-to-noise ratio and results in a lower bound for the performance metrics, such as outage probability and average error probability. In this paper, a framework is introduced to obtain a tight upper bound for these performance metrics, as a function of harmonic mean approximation. It is shown that this upper bound is the tightest possible one among all harmonic mean related approximations. This bound is derived by modifying the same analysis used in the previous studies to compute the lower bound, without increasing the order of computational complexity. Numerical results and simulations show that the proposed upper bound for the performance metrics well follows the exact values.

Outage probability of dual-hop AF opportunistic relaying with directional antennas

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.

On the Statistics of MFR Routing in One-Dimensional Ad Hoc Networks

The performance analysis of a wireless network significantly depends on the routing-related statistics. Power consumption, multihop communication delay, and position estimation are among the parameters that are affected by the routing scheme. In this paper, statistical parameters of the most forward within range routing in 1-D ad hoc networks are investigated. Several parameters, such as the probability mass function (pmf) of the number of broadcast hops, the probability density function of the connectivity distance for a given number of hops, and the pmf of the number of hops between the source and the destination, are derived. For cases where the exact analytical results are recursive and complicated, good approximate nonrecursive formulas are also derived. We verify the correctness of the exact formulas and the precision of the approximate results by simulations. Some applications of the derived statistical parameters are also presented.

Probability of outage in a clustered poisson field of interfering nodes

In this paper, the interference statistics and the probability of outage in a clustered Poisson field of interfering nodes are analyzed. In this architecture, a large number of users communicate directly with each other through their closest cluster heads. It is assumed that the location of the users and the cluster heads are two independent two-dimensional homogeneous Poisson point processes over an unbounded plain. A common bandwidth is shared among all users and the transmitted signals undergo path loss and Log-normal shadowing. A perfect power control is assumed in a user to cluster head transmission. We analyze the performance of this wireless network by calculating the probability of outage over a cluster head. To this end, we derive analytical formulas for the mean and the variance of the total amount of interference. Further, we show that the total interference received by the cluster head precisely follows Lognormal distribution. The accuracy of Log-normal assumption as well as the obtained analytical results are verified by simulations.

Performance Analysis of Hybrid CDMA Systems

In this paper, a hybrid wireless CDMA network composed of ad hoc relays overlaid on a conventional CDMA cellular network is considered. In this setting, effective relaying helps reduce the level of interference at the base stations. The goal of this paper is to investigate the performance improvement in hybrid networks as quantified by the reduction in the probability of outage over the base stations due to interference. A new approximation method to analyze this probability and the average number of active users is introduced. Numerical results and simulations verify the extensive gain obtained by employing ad hoc relaying over the conventional CDMA networks. Moreover, results illustrate the excellent accuracy of the presented analytic approach.

Correction to "Novel Representations for the Bivariate Rician Distribution" [Nov 11 2951-2954]

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.