Sharif Digital Repository

In this short paper, we study the deafness problem raised in the directional multi Gigabit transmission of IEEE 802.11ad standard which causes the devices to experience unequal chance of accessing the medium. We define three groups of Quasi-Omni (QO) antennas and propose two simple approaches to mitigate the deafness problem. Our simulation results show that the fairness increases up to 99% compared with current definition of IEEE 802.11ad which is less than 40%. © 2017 IEEE  

Let P be a set of points in the plane, each equipped with a directional antenna that can cover a sector of angle α and range r. In the symmetric model of communication, two antennas u and v can communicate to each other, if and only if v lies in u’s coverage area and vice versa. In this paper, we introduce the concept of fault-tolerant spanners for directional antennas, which enables us to construct communication networks that retain their connectivity and spanning ratio even if a subset of antennas are removed from the network. We show how to orient the antennas with angle α and range r to obtain a k-fault-tolerant spanner for any positive integer k. For α ≥ π, we show that the range 13 for... 

Let P be a set of points in the plane, each equipped with a directional antenna that covers a sector of angle α and range r. In the symmetric model of communication, two antennas u and v can communicate to each other, if and only if v lies in u's coverage area and vice versa. In this paper, we introduce the concept of fault-tolerant spanners for directional antennas, which enables us to construct communication networks that retain their connectivity and spanning ratio even if a subset of antennas are removed from the network. We show how to orient the antennas with angle α and range r to obtain a k-fault-tolerant spanner for any positive integer k. For α≥π, we show that the range 13 for the... 

We consider a source model for information theoretic secret key agreement based on the distance among the nodes, in a basic system consisting of two legitimate users and an eavesdropper. The legitimate nodes try to agree on a reliable and secure key based on their noisy observation of distance between them. We propose two methods to enhance system utility: 1) Artificial Noise Forwarding (ANF), 2) transmission in different beam directions (multi-antenna transmission). In the first method artificial noise is used to worsen e a vesdropper's distance estimation and in the second method beacon signals are sent in different directions and the virtual distances in different beam directions are used... 

This study presents an efficient fractional frequency reuse scheme for macrocell network which uses six directional antennas to cover the outer region and analyses the performance. Cross-tier interference between macrocell and femtocell networks leading to throughput and outage probability degradation is a major issue in two-tier networks when femtocells are deployed in co-channel with macrocells. In this study, the received interference from the macrocell network to femtocell network is analysed. Then, based on the degree of received interference, an algorithm for orthogonal resource allocation to femtocells with low cross-tier interference is presented. According to the introduced scheme,... 

The authors propose a novel solution for decorrelating closely spaced antennas with identical radiation patterns. By proper steering of the directional elements' patterns, the decorrelation distance is reduced to 0.25λ in comparison with the well-established 0.4λ result based on the Bessel-shaped correlation expression. In addition, by proposing the definition of Decorrelation Factor of an antenna pattern, a framework for comparison of correlation behaviour of different antennas is provided. Subsequently, a performance metric characterised by the Jensen upper bound for the capacity of closely spaced antennas is proposed. Finally, we apply our results to two practical directional antennas,... 

In this paper, we evaluate the capacity of Multiple-Input Multiple-Output (MIMO) systems using directional antennas in non-isotropic scattering environments. Our analytical analysis approach results in closed-form approximate formulas in low Signal to Noise Ratio (SNR) regime (in contrast to previous research works which have investigated the same problem by employing experimental or simulation frameworks). We propose an upper bound for the introduced approximate error. Our results show that MIMO systems equipped with directional antennas may have much higher capacity in nonisotropic scattering environments compared to MIMO systems equipped with omni-directional antennas. We also evaluate... 

One of the intrinsic problems of mobility in wireless networks is the discovery of mobile nodes. A widely used solution for this problem is to use different variations of beacons, such as hello packets. Although a poorly designed beaconing scheme may lead to unnecessary energy usage or poor throughput, a systematic approach to analyze and select beaconing parameters is not provided in the literature. Here, we propose a model to study the beaconing efficiency using some measures such as the link lifetime, the probability of link establishment, and the delay to discover a new neighbor. The model is general and does not adhere to any particular mobility model; the only input from the mobility... 

We study hybrid digital-analog (HDA) joint source-channel coding schemes in transmitting an analog Gaussian source over an AWGN channel in the presence of an interference, correlated with the source. We analyze these schemes to obtain achievable (mean-squared error) distortion-power tradeoffs. For comparison, we also obtain two outer bounds for the achievable distortion-power tradeoff; those are two necessary conditions under which (D,P) is achievable. Using numerical examples, we demonstrate that, a two-layered coding scheme consisting of analog and Costa coding performs well compared to other provided HDA schemes  

In smart antenna systems, The localization and direction of desired source(s) must be known. In this paper, we introduce a method called "DMSAE" (Direction finding of Multiple Sources by Alternating Eliminations) to find the radio directions of signals impinging on an arbitrary antenna array and the number of the signals. This method which is based on the Minimum Variance Distortionless Response (MVDR) algorithm, can not only detect the direction and the number of sources, simultaneously, but also has better resolution ability compared to the other conventional direction finding algorithms. This method can also detect very weak sources when other powerful sources exist in the environment. In... 

To evaluate the performance of the distributed medium access control layer of the emerging ultrawideband and 60-GHz millimeter wave (mmWave) wireless personal area networks based on ECMA-368 and ECMA-387 standards, the first step is to determine the beacon period length (BPL) of the superframe in a given network. In this paper, we provide an analytical model for the probability mass function (PMF) of the BPL as a function of the network dimensions, number of beaconing devices, antenna beamwidth, and the transmission range of the devices. To enable devices with steerable directional antennas in the ECMA-387 standard to have simultaneous communications with neighbors in their different antenna... 

Performance of routing is severely degraded when misbehaving nodes drop packets instead of properly forwarding them. In this paper, we propose a Game-Theoretic Adaptive Multipath Routing (GTAMR) protocol to detect and punish selfish or malicious nodes which try to drop information packets in routing phase and defend against collaborative attacks in which nodes try to disrupt communication or save their power. Our proposed algorithm outranks previous schemes because it is resilient against attacks in which more than one node coordinate their misbehavior and can be used in networks which wireless nodes use directional antennas. We then propose a game theoretic strategy, ERTFT, for nodes to... 

A novel, robust and practical method for active user enumeration in asynchronous CDMA in multipath channel condition is proposed in this paper. Most of the previous works do not consider the fact that in practical case, user's signals with the help of receiver arrive asynchronously. The proposed method can be used practically in blind multi-user detection such as eavesdropping; moreover, the method is based on information theory criteria which outperform other methods. Minimum description length (MDL) has better performance than all other information criteria used in such scenarios. Unlike most of the pervious works, we do not exploit array antenna to gather necessary data of the users.... 

We study transmission of a memoryless Laplacian source over an average-power limited additive white Laplacian noise (AWLN) channel under bandwidth compression in two cases: 1) matched signal-to-noise ratio (SNR), 2) mismatched SNR. A hybrid digital-analog (HDA) joint source-channel coding (JSCC) scheme is proposed and show that this scheme can achieve a distortion very close to the lower bound on mean-absolute error (MAE) distortion under matched SNR conditions  

We consider transmission of a Gaussian source over a Gaussian channel under bandwidth compression in the presence of an interference known only to the transmitter. We study hybrid digital-analog (HDA) joint source-channel coding schemes and propose two novel layered coding schemes that achieve the optimal mean-squared error (MSE) distortion. This can be viewed as the extension of results by Wilson ["Joint Source Channel Coding With Side Information Using Hybrid Digital Analog Codes," IEEE Trans. Inf. Theory, vol. 56, no. 10, pp. 4922-2940, Oct. 2010], originally proposed for sending a Gaussian source over a Gaussian channel in two cases: 1) Matched bandwidth with known interference only at...