Sharif Digital Repository

Chemical reactions are a prominent feature of molecular communication systems, with no direct parallels in wireless communications. While chemical reactions may be used inside the transmitter nodes, receiver nodes, or the communication medium, we focus on its utility in the medium in this paper. Such chemical reactions can be used to perform computation over the medium as molecules diffuse and react with each other (physical-layer computation). We propose the use of chemical reactions for the following purposes: 1) to reduce signal-dependent observation noise of receivers by reducing the signal density; 2) to realize molecular physical-layer network coding (PNC) by performing the natural XOR... 

Wireless body area networks (WBANs) are characterized by short-range wireless communication between inherently resource-limited sensors that operate in the vicinity of the human body for recording certain physiological signals. One of the main limitations of WBANs is in terms of their available power. Since the nodes are typically battery-driven, an efficient power transmission is essential to guarantee long-lasting communications among nodes without the need for frequent battery replacement or charging. In this study, aiming to improve the WBAN performance, we first investigate the power allocation problem by choosing the ergodic capacity and the outage probability as the desired metrics.... 

Generalized frequency division multiplexing (GFDM) is one of the multicarrier modulation candidates proposed for the 5th generation of wireless networks. Among GFDM linear receivers, GFDM MMSE receiver achieves the best error performance for multipath fading channels at the cost of high numerical complexity. Hence, the combination of GFDM match filter (MF) receiver and double-side successive interference cancellation (DSIC) method is used instead. However, there is a significant gap between the error performance of GFDM MMSE and DSIC/MF receivers for the case of employing modern channel coding. Recently, we have proposed a new multicarrier scheme based on GFDM architecture called generalized... 

To support the increasing data traffic demand in wireless communications networks, a multi-tier architecture that consists of multiple small cells is adopted in traditional (macro) cellular networks. Nevertheless, due to the expansion of various wireless devices and services, there is still a need to increase the network capacity in new generation networks such as 5G. Hence, the integration of Device-to-Device (D2D) communication as a promising technology with heterogeneous networks has been proposed. This integration not only increases network capacity but also improves spectral efficiency and alleviates the traffic load of base stations. However, the co/cross-tier interferences between D2D... 

In this letter, a compact, wideband, and fully planar microstrip crossover structure is proposed. This design is based on a compact microstrip to coplanar waveguide transition, which has a measured bandwidth extending from dc to 40 GHz. At 20 GHz, the measured insertion loss, return loss, and isolation are better than 0.35, 21, and 19 dB, respectively. This circuit is ultracompact with the core size of 3 mm ×3 mm, which is 0.2λ×0.2 λ at 20 GHz. © 2012 IEEE  

The conventional time-modulated arrays (TMAs) have a low radiation efficiency, since each antenna turns off at specific time slots. In this paper, first, the efficiency of TMA is investigated analytically. Next, the optimized switching sequences are proposed to enhance the radiation efficiency of a specific sideband, while preserving the level of the other sidebands. The practical hardware limitations are considered in the switching sequence design. Moreover, a low-cost flexible eight-element printed dipole array operating at 1.2-1.4 GHz is implemented to verify the proposed algorithms. The measured radiation patterns indicate that by applying the proposed sequences, the TMA efficiency... 

The vision of advanced long-term evolution (LTE-A) project is set to ultimate increase of network capacity in heterogeneous networks (HetNets). In HetNets with small cell configuration, a considerable majority of user devices is eventually connected to the macrocell base station (MBS), while small base stations (BSs), such as femtocell access points (FAPs), are still without any user. This results in unbalanced load and reduces the data rate of macrocell user equipment (MUE). In this paper, a method is proposed for load balancing among FAPs, while desired throughput is achieved. The proposed method uses the estimated received signal strength from different BSs and adjusted pilot signals.... 

Centralized coded caching and delivery is studied for a partially-connected fog radio access network (F-RAN), whereby a set of H edge nodes (ENs) (without caches), connected to a cloud server via orthogonal fronthaul links, serve K users over the wireless edge. The cloud server is assumed to hold a library of N files, each of size F bits; and each user, equipped with a cache of size MF bits, is connected to a distinct set of r ENs; or equivalently, the wireless edge from the ENs to the users is modeled as a partial interference channel. The objective is to minimize the normalized delivery time (NDT), which refers to the worst case delivery latency, when each user requests a single file from... 

Energy Harvesting (EH) is a novel technique to prolong the lifetime of the wireless Ad-hoc and sensor networks with replenishable nodes. In this sense, it has emerged as a promising technique for Green Communications. On the other hand, cooperative communication with the help of relay nodes improves the performance of wireless communication networks. In this paper, we investigate the cooperation in EH nodes. We consider the optimal power and rate allocation in the full-duplex Gaussian relay channel in which source and relay can harvest energy from their environments. In our model, the energy arrivals at the source and the relay are general stochastic processes with known EH times and amounts... 

We consider a slotted Aloha-based wireless communication network comprising a source and an active relay, both transmitting to a common destination. The relay node is able to relay the unsuccessfully transmitted packets of the source node, if it can detect them. We find the analytical closed form optimal static relaying policy in order to minimize the average transmission delay (ATD) of source packets, while ATD of its own packets is constrained. A static relaying policy is determined by acceptance and relaying probabilities of the relay node. According to acceptance probability, the relay node decides whether to accept an unsuccessfully transmitted packet from source or not, while the... 

Vehicular ad-hoc networks (VANETs) are under active development, thanks in part to recent advances in wireless communication and networking technologies. The most fundamental part in VANETs is to enable message authentications between vehicles and roadside units. Message authentication using proxy vehicles has been proposed to reduce the computational overhead of roadside units significantly. In this message authentication scheme, proxy vehicles that verify multiple messages at the same time improve roadside units' efficiency. In this paper, first we show that the only proxy-based authentication scheme (PBAS) presented for this goal by Liu et al. cannot guarantee message authenticity, and... 

Wireless body area networks (WBANs) are characterized by short-range wireless communication between inherently resource-limited sensors that operate in the vicinity of the human body for recording certain physiological signals. One of the main limitations of WBANs is in terms of their available power. Since the nodes are typically battery-driven, an efficient power transmission is essential to guarantee long-lasting communications among nodes without the need for frequent battery replacement or charging. In this study, aiming to improve the WBAN performance, we first investigate the power allocation problem by choosing the ergodic capacity and the outage probability as the desired metrics.... 

In this paper, we study the cell planning problem for a two-tier cellular network containing two types of base stations (BSs)— i.e. with fiber backhaul, referred to as wired BSs (W-BSs), and BSs with wireless backhaul, referred to as unwired-BSs (U-BSs). In-band full-duplex wireless communications is used to connect U-BSs and W-BSs. We propose an algorithm to determine the minimum number of W-BSs and U-BSs to satisfy given cell and capacity coverage constraints. Furthermore, we apply our proposed non-dominated sorting genetic algorithm II (NSGA-II) to solve the joint cell and backhaul planning problem to minimize the cost of planning, while maximizing the coverage simultaneously.... 

A conventional wireless sensor network node consists of a number of components: microprocessor, memory, sensor, and radio. Advances in nanotechnology have enabled the miniaturization of these components, thus enabling wireless nanoscale sensor networks (WNSN). Due to their small size, WNSN nodes are expected to be powered by harvesting energy from the environment. Unfortunately, there is a mismatch in the energy that can be harvested and the energy required to power all the aforementioned components in a WNSN node. In this article, we propose a simplified sensor node architecture for event detection. We call our architecture Sensorless Event MONitoring in self-powered WNSNs (SEMON). A SEMON... 

Two gains play key roles in recently developed multiple-input-multiple-output (MIMO) wireless communication systems: 'spatial diversity' gain and 'spatial multiplexing' gain. The diversity gain (DG) refers to the capability to decrease the error rate of the MIMO channel, whereas the multiplexing gain (MG) implicitly refers to the amount of increase in the capacity of the MIMO channel. It has been shown that there is a fundamental tradeoff between these two types of gains, meaning interplay between increasing reliability (via an increase in the DG) and increasing data rate (via an increase in the MG). On the other hand, recently, MIMO radars have attracted much attention for their superior... 

To cope with the unprecedented growth of mobile data traffic, we investigate the performance gains obtained from unifying coverage-centric 4G mobile networks and capacity-centric fiber-wireless (FiWi) broadband access networks based on data-centric Ethernet technologies with resulting fiber backhaul sharing and WiFi offloading capabilities. Despite recent progress on backhaul-aware 4G studies with capacity-limited backhaul links, the performance-limiting impact of backhaul latency and reliability has not been examined in sufficient detail previously. In this paper, we evaluate the maximum aggregate throughput, offloading efficiency, and in particular, the delay performance of FiWi enhanced... 

In this paper, we analyze the saturation throughput of a cognitive WLAN overlaid on a primary OFDMA TDD network (e.g., LTE or WiMAX). In this scenario, after the contention among the secondary nodes, the winner node transmits its data packet in the empty resource blocks (RBs) of downlink and uplink subframes of the primary network. Regarding the OFDMA structure as well as time-scheduled resources in the primary network, the time duration of opportunities for the secondary network does not follow simple exponential on-off pattern. To model the dynamic behavior of opportunities for secondary nodes as well as contentions to exploit the opportunities, we propose an analytical model comprised of... 

Energy harvesting has been developed as an effective technology for communication systems in order to extend their lifetime. In this paper, we consider a single-user energy harvesting wireless communication system, in which arrival data and harvested energy curves are modeled as continuous functions. Our first goal is to find an offline algorithm, which maximizes the amount of data, which is transmitted to the receiver node by a given deadline. If more than one scheme exists that transmits the maximum data, we choose the one with minimum utilized energy at the transmitter node. We find this optimal algorithm, by showing its properties. Next, we propose an online algorithm for this system and... 

Matching theory is a powerful tool to study the formation of dynamic and mutually beneficial relations among different types of rational and selfish agents. It has been widely used to develop high performance, low complexity, and decentralized protocols. In this article, a comprehensive survey of matching theory, its variants, and their significant properties appropriate for the demands of wireless communications and network engineers is provided. Recent research progress in applying matching theory to wireless communications to address major technical opportunities and challenges is presented. A novel classification of matching models from the practical perspective is provided, and the... 

We characterize terahertz wireless channels for extracting data from nanoscale sensors deployed within human lungs. We discover that the inhalation and exhalation of oxygen and carbon dioxide causes periodic variation of the absorption coefficient of the terahertz channel. Channel absorption drops to its minimum near the end of inhalation, providing a window of opportunity to extract data with minimum transmission power. We propose an algorithm for nanosensors to estimate the periodic channel by observing signal-to-noise ratio of the beacons transmitted from the data sink. Using real respiration data from multiple subjects, we demonstrate that the proposed algorithm can estimate the minimum...