The Modares Journal of Electrical Engineering
Volume:16 Issue: 2, 2016

In recent years, Underwater Acoustic Communications (UAC) has been a great matter of consideration because of its importance in different areas such as commercial and military applications. Underwater acoustic communications channel is known as a time-varying and doubly selective channel in both time and frequency domains. The orthogonal frequency division multiplexing (OFDM) modulation is an effective technique to communicate over challenging acoustic channels. In addition, using multiple-input multiple-output (MIMO) systems increases channel capacity which results in high data rate communications. Recently, basis expansion models (BEMs) have been widely used to estimate an underwater acoustic channel. In particular, when the channel is time-varying, the BEM model can effectively estimates the channel with a reduced number of coefficients and low computational complexity. To improve the performance of a MIMO communication channel, various beamforming techniques have been proposed in different areas. Inspired by the basis expansion modeling of an underwater acoustic channel, in this paper we develop a BEM based adaptive space-time beamforming for both the transmitter and receiver of an UAC. The Laguerre basis expansion model is employed in the linearly constrained minimum variance (LCMV) beamformer to obtain an adaptive scheme for updating the beamforming weights at the transmitter and receiver and to optimize the system performance in real-time. Our Simulation results show that the proposed BEM based beamformer method improves the Bit-Error-Rate (BER) and Minimum-Square-Error (MSE) performance substantially for a Rayleigh fading underwater acoustic channel. In particular, our method improves the BER and MSE about 10dB and 4dB compared to the discrete prolate spheroidal sequence (DPSS) method.

In this paper, we consider 5G as an evolution of 4G, thus we propose logical connections between LTE-A entities such as SGW, PDN firstly. Then, we present a new configuration and accordingly data/control realization of 5G EPS (Evolved Packet System) based on a carrier-grade hypervisor and an intelligent core server (IC server) to provide virtualization and flexibility to the network. In addition, we define two new entities hAN (heterogeneous access network) and TNT-Gateway (TENANT Gateway) for access and core, respectively and define their functions and data/signaling connections. Some important advantages of these configurations are: 1) cost reduction, 2) network efficiency improvement, and 3) increase of network flexibility and service availability which approaches LTE to 5G.

This work presents a fully integrated 8-12 GHz fractional-N frequency synthesizer (FNPLL) for using in communication satellites. The FNPLL implemented in a 90-nm standard CMOS technology. The simulation results demonstrate that the Voltage Controlled Oscillator (VCO) has a phase noise of -106 dBc/Hz at 1-MHz offset for a 10 GHz Local Oscillator (LO) signal, and the higher fractional spur is -55 dBc in a 10-GHz LO signal. The proposed FNPLL consumes 5.029-6.579 mW from 1.2-V power supply and has a phase noise of -70 dBc/Hz, -88 dBc/Hz and -116 dBc/Hz at 10-KHz, 100-KHz and 1-MHz offsets, respectively.

In this letter, we propose a novel frequency reconfigurable antenna design for aircraft and drone telecommunication that covers the applied VHF/UHF/L- bands. The proposed structure is a Reduced-Size Edge-Shorted dipole/monopole antenna and consists of metallic line, notch, and metal reflector, making it easy to combine directional, high-gain, low cross-polarization and wide bandwidth. The antenna is frequency-reconfigurable using a PIN diode switch. In the ON state, the antenna operates as a dipole-traveling antenna and covers 30–400 MHz. In the OFF state, the antenna operates as an Edge-Folded monopole antenna and covers 500–1220 MHz. This work proposes a technique for size reduction using side slot and for gain equalization using switchable folded wing based on Smart Geometry Reconfiguration. The proposed antenna has VSWR

In this paper, we consider a price-based resource allocation within an Orthogonal Frequency-Division Multiple Access (OFDMA) based on spectrum sensing in the cognitive networks. Furthermore, there is the primary network which has an opportunity to sell the spectrum to secondary network. We assume the secondary network’s interference pricing is used to protect primary network and propose a joint utility maximization of the primary and secondary with a maximum interference constraint at the primary and a transmission power threshold at the secondary transmitter. Accordingly, we devise a novel cost computation strategy which is function of primary and secondary behaviors. To formulate this method, a Stackelberg game and equilibriums are exploited. Numerical results are presented to verify the proposed scheme. The impact of different system parameters is investigated and compared through simulations.

In this paper, we study the physical layer security in the presence of an adversary which is able to switch its mode from jamming mode (when transmits jamming signals) to eavesdropping mode (when adversary eavesdrops legitimate link) and vice versa. To combat with this type of adversary and establish security in this communication, we propose two approaches: 1) probabilistic approach (PA), 2) worst case approach (WCA). The system model consists of a source, an adversary and full-duplex destination. A full duplex destination can receive the private message and transmit jamming signal to deceive the adversary, simultaneously. The simulation results show that the average rate PA, is 50% more than the WCA.

To address the continuously increasing demand for high data rates, beside air interface technologies, there are requirements to introduce new and effective ways to design architecture of networks. This paper proposes several technologies which can be used as promising candidates to change the future of wireless communication architecture especially in Fifth generation (5G) wireless network. In this article, we discuss various promising cellular architectures such as full duplex communication, device-to-device communication, mobile femtocell, visible light communication and visualization in 5G.

Due to the influence of Internet and mobile service in every part of our lives in addition to pervasive demand for them, next generation wireless networks should be able to address different kind of objectives or demands. New generation of cellular networks must achieve high user quality of experience (QoE) in order to satisfy the user demands and survive in market. To meet this demands, drastic revision need to be made in previous network architecture. This paper reviews some of the key technologies which are emerged to improve future network architecture and meet the demands of users, especially in Fifth generation (5G) cellular network. In this paper, the prime focus is on the air interface of 5G which includes millimeter wave communication, multiple access technologies, carrier aggregation (CA), and massive Multiple-Input Multiple-Output (MIMO).

This paper addresses the problem of inter-flow network coding for unicast sessions in lossy channel wireless networks. In spite of decreasing the number of transmissions, network coding intuitively increases the sensitivity of nodes to lost packets. First of all, coded packets carry more information than native packets and thus losing a coded packet prohibits a series of dependent nodes from decoding their intended packets. Secondly, for the scheme with opportunistic listening, it is necessary for some of the nodes to overhear the transmission of their neighbors. Thus, successful decoding requires overhearing of the corresponding packet(s) in addition to correct reception of unicast and broadcast transmissions. In this paper, we study the effect of lossy channel on the aggregate network throughput in the presence of network coding. We provided a linear programming formulation to compute the throughput performance of network coding for a general lossy wireless network. Further, we consider a retransmission mechanism for both unicast and broadcast. Our LP system supports both COPE and Star coding schemes. The advantages of the proposed NC schemes over the non-NC ones are shown through simulations and theoretical analysis. Results show that network coding can boost the capacity of wireless network up to 40% under lossy channel condition.

Connected dominating set (CDS) problem is the most widely used method for backbone formation ‎in wireless sensor networks. To date, numerous algorithms have been proposed for backbone ‎construction on minimum CDS (MCDS) problem in unit disk graphs (UDG); however, only a few ‎algorithms have been proposed on MCDS problem in disk graphs with bidirectional links (DGB) ‎and on degree-constrained minimum-weight CDS (DC-MWCDS) problem in UDG. To the best of ‎our knowledge, no work has been done on DC-MWCDS problem in DGB. In this paper, we present ‎OEDC-MWCDS problem (optimal energy and degree constrained minimum-weight connected ‎dominating set) for constructing energy efficient backbone in wireless sensor networks. Then, we ‎model a wireless sensor network as a disk graph with bidirectional links and propose a backbone ‎construction algorithm called EBC-PSO (Energy efficient Backbone Construction utilizing Particle ‎Swarm Optimization algorithm) to obtain a CDS with the minimum weight subject to the optimal ‎energy and degree constraint. The main objective of the proposed algorithm is to find the optimal ‎values of energy and degree of constraint to maximize network lifetime. In the proposed algorithm, ‎optimal coefficients of minimum remaining energy and maximum degree of nodes are determined ‎utilizing PSO algorithm. Then, in the selection of DS nodes, these coefficients are used. Simulation ‎results verify the performance of the proposed algorithm in terms of network lifetime and ‎backbone size.‎