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The modern communication systems need development in antennas which have large bandwidth and low profile. Profile is the physical size of the antenna and it should be as small as possible for easy installation and operation. The paper deals with design aspects of square microstrip patch antenna with proximity feed and its properties. In this paper, simulations are carried out on C-band square microstrip patch antenna that suits Wi-Fi and bluetooth applications. With the adjusted parameters, the designed antenna exhibits maximum gain of 7 dBi and return loss -40 dB at center frequency 5 GHz. Desired patch antenna design was simulated using ANSYS HFSS software. The substrate material used for designing of microstrip patch antenna is RT Duroid 5880 and the thickness of the substrate is 1.6 mm. [ABSTRACT FROM AUTHOR]

Transmission Control Protocol (TCP) is a communications standard that enables application programs and computing devices to exchange messages over a network. Since the 1970s, several TCP variants have been introduced to deal with the fast increasing network capacities, especially in high Bandwidth Delay Product (high-BDP) networks. The different variants are: TCP Tahoe, TCP Reno, TCP New Reno, TCP Linux, TCP Vegas, TCP Sack, etc. TCP provides the quality of performing consistently well and End-To-End (ETE) delivery of packets in the network. Each of these TCP variants has its own mechanism against the problem, some of these approaches can estimate available bandwidths and some react based on network loss and/or delay changes. It is essential to perform a comparison between the high-speed TCP variants that have a high standard of importance, especially after a quick growth of networks bandwidths. In this paper, TCP variants that are implemented in Linux have been evaluated using NS2 network simulator. This performance evaluation presents the advantages and disadvantages in terms of Packet Delivery Ratio (PDR), ETE delay and throughput using different applications like File Transfer Protocol (FTP), Simple Mail Transfer Protocol (SMTP) and Hyper Text Transfer Protocol (HTTP). [ABSTRACT FROM AUTHOR]

The paper studies the application of fuzzy set optimization techniques for the reconfiguration of optical internets using Internet Protocol (IP) over Wavelength Division Multiplexed (WDM) (IP-over-WDM) technology. The IP-over-WDM networking technology with terabits per second bandwidth become a natural choice for the future generation internet networks (optical internets), Wide Area Network (WAN) environments and backbone networks due to its potential ability to meet the rising demand of high bandwidth and low latency communication. Recently, Virtual Topology Reconfiguration (VTR) of IP-over-WDM networks has received greater attention among researchers. Fuzzy set finds many applications in the field of network engineering, which includes linear programing, traffic prediction, network modeling, traffic modeling, etc. In this paper, we have presented a new approach for reconfiguring virtual topology of IP-over- WDM networks using fuzzy set optimization technique. The computed results show that this new approach achieves better performance in terms of computational accuracy, number of changes and Average Weighted Hop Count (AWHT). [ABSTRACT FROM AUTHOR]

The paper describes the effect of with and without dielectric superstrates on bandwidth, beamwidth, gain, resonant frequency, input impedance, return loss, Voltage Standing Wave Ratio (VSWR) and radiation pattern of rectangular microstrip patch antenna. It is found that there is a slight degradation in the performance of the antenna when the superstrate is touching the patch antenna. In particular, the resonant frequency decreases with increase in the dielectric constant of the superstrate thickness. In addition, it has also been observed that return loss and VSWR increase, however, bandwidth and gain decrease with the dielectric constant of the superstrate thickness. The microstrip patch antenna without dielectric superstrate achieves an impedance bandwidth of 0.203 GHz (SWR < 2) at 2.4 GHz, compared to microstrip patch antenna with dielectric superstrate, which shows that the resonate frequency is decreased to 2.31 GHz from 2.40 GHz, impedance bandwidth to 0.040 GHz from 0.200 GHz (SWR < 2) at 2.30 GHz and the gain to 2.80 GHz from 7.30 GHz. The optimum gain is obtained at ∊r2 = 2.2. This type of antenna is mainly used in wireless and Bluetooth applications. [ABSTRACT FROM AUTHOR]

In this paper, three millimeter wave antennas are presented for 60 GHz. Each antenna is an array of 2 x 2 microstrip antennas. All three antennas utilize thin substrate of RT Duroid 5,880 having permittivity εr = 2.2. The basic design of 2 x 2 array antenna utilizing RT Duroid is extended for two superstrate loaded antennae designs. The first design uses foam and the other design uses RT Duroid with air gap as superstrates. 2 x 2 array patch engraved on RT Duroid above ground plane acts as driven patch, while the patch incised upon the superstrate acts as a parasitic patch. Optimization of the basic design achieves highest gain in millimeter wave region, whereas the superstrate loaded design results in a much wider bandwidth. A comparison of all design configurations is carried out through the sensitive study of the simulation results, including return loss, polarization and radiation patterns, which validates the designs for millimeter wave region. [ABSTRACT FROM AUTHOR]

Survivability is an issue of great concern in high speed networks. Optical Packet Switching (OPS) is an established technique in the area of survivable high speed future networks. In this paper, network performance is evaluated in response to ingress packet size variation. The performance is evaluated for both protocols: Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). Analysis is performed on mesh networks for different ingress packet size. Response of both transport layer protocols has been observed under single link failure. Network throughput with TCP is higher as compared to throughput with UDP. Network throughput is highest at 500 byte packet size, which is less than the configured Maximum Segment Size (MSS) of transport layer protocols. [ABSTRACT FROM AUTHOR]

The common approach to realizing high gain is to use several low gain elements in an array either in linear, rectangular or circular manner. Linear arrays are used for producing narrow beam in plane parallel to the antenna axis, while wider beam in orthogonal plane. Complexities in the practical implementation of arrays make it less attractive to antenna designers. An array of efficient radiators with an efficient feed network and coarse fabrication tolerances would satisfy these requirements. In the paper, first linear array of 4 cylindrical dielectric resonator elements with uniform excitation has been designed and investigated. Later, in the same arrangement, array elements are excited according to Dolph-Chebyshev distribution for a set of optimum beam width and side lobe level. Array has shown beam width of 24o with side lobe level of 18 dB in H-plane with gain of 10 dB, whereas in E-plane, peak of 12 dB has shown beam width of 23o. Tapering in excitation is achieved with the feed network itself and hence no additional element is needed to obtain the different level of excitation. The proposed design with impedance bandwidth of 1 GHz and gain of nearly 12 dB can be used for satellite communication and other wideband wireless applications at X-band. [ABSTRACT FROM AUTHOR]

This paper experimentally studies a simple slot-fed Cylindrical Dielectric Resonator Antenna (CDRA). The antenna consists of a Cylindrical Dielectric Resonator (CDR) fed by a microstrip line feed through a coupling slot. The study is carried out by using three antennas with different Dielectric Resonator (DR) thickness and provides dual bands with improved bandwidth. It is observed that the impedance bandwidth increases from 37.09% to 70.9% as the thickness of DR is increased. The return loss and radiation patterns of the proposed antennas are measured and presented. [ABSTRACT FROM AUTHOR]

The demand for high speed networks has significantly increased. In order to supply network capacity to attend to this demand, optical networks have been considered as the most reliable and economic solution to provide high transmission rates. High speed network works efficiently with appropriate routing techniques. The objective of this paper is to calculate and compare the performance of static routing techniques and dynamic routing techniques in wired networks. The effect of variations in bandwidth and number of nodes on the network performance are analyzed over a wide range of values. The parameters used for evaluation of performance are throughput, packet loss ratio, average latency and average jitter. Simulations are performed and analyzed in NS-2.35, and it is concluded that dynamic routing protocol shows better results as compared to static routing protocol network sizes considered. As network size increases, dynamic routing proves to be even more efficient. [ABSTRACT FROM AUTHOR]

As the demand for high data rates continues to grow, advanced modulation formats must be adapted to support high data rates in optical communication system. Optical-Orthogonal Frequency Division Multiplexing (OFDM) is a promising technology providing support to high data rates and high tolerance to channel dispersion with high spectral efficiency. Further, advanced modulation techniques such as Quadrature Phase Shift Keying (QPSK) and 16-QAM have a greater effect on the performance of optical-OFDM system. QPSK modulation technique can be used to achieve high spectral efficiency, limited only by the noise level of the communication channel. M-Quadrature Amplitude Modulation (QAM) modulation techniques have high spectral efficiency in each subcarrier of the OFDM signal and this high spectral efficiency helps to support high data rate with the same low bandwidth optical components used at lower data rates. This paper presents an optical-OFDM system model for both QPSK and 16-QAM modulation techniques. The various performance parameters such as BER, Q factor, eye opening and jitter of optical-OFDM system are also analyzed for both modulation techniques. The effect of increase in modulation order M of M-QAM is also analyzed on the system data rate, while keeping the same data bandwidth. [ABSTRACT FROM AUTHOR]

Orthogonal Frequency Division Multiplexing (OFDM) is an efficient method of data transmission for high-speed communication systems over multipath fading channels. It is a bandwidth-efficient multicarrier modulation where the available spectrum is divided into many subcarriers. It has gained a wonderful significance in recent years because of its robustness in the presence of severe multipath channel conditions with simple equalization, toughness against Inter-Symbol Interference (ISI) and multipath fading, in addition to its high spectral competence. The Peak-to-Average Power Ratio (PAPR) is a major drawback of multicarrier transmission system such as OFDM. In this paper, the authors propose PAPR reduction in OFDM using companding technique with Kalman filter to decrease the nonlinear distortion and to improve the power efficiency of the nonlinear High Power Amplifier (HPA). When companding is introduced in the OFDM system, the OFDM system is able to operate nearer to saturation without substantial transmit distortion. Therefore, it is found that companding can provide very modest performance gains in comparison to systems that do not employ companding. The performance of companding algorithm with Kalman filter that introduced better PAPR reduction of 4.3 dB can be achieved for suitable low power consumption communication system. [ABSTRACT FROM AUTHOR]

A communication system has to operate only on the assigned band to avoid interference with another system. To provide services to the new added users on the given limited spectrum requires a more efficient use of the radio spectrum. Spatial signal processing can efficiently make use of the radio spectrum and can provide solutions to fading and multipath propagation which normally occur in wireless communications. Wider coverage and higher transmission rate can also be achieved with spatial signal processing. Spatial signal processing and diversity reception can be achieved with an efficient design of the smart antenna. Due to advancement in low-cost digital signal processors and innovative software-based signal processing techniques, the smart antenna systems have received enormous interest worldwide during the past decade. They have been extensively employed in several applications such as mobile communication, mobile wireless ad-hoc network, cognitive radio and mobile satellite. All applications are based on the efficient design of smart antenna systems. The multirate digital signal processing offers a reduced computation complexity for the given task and reduced transmission rate. This paper investigates the work done on smart antenna during the last decade and discusses the application of multirate signal processing in smart antenna. [ABSTRACT FROM AUTHOR]

The paper presents two heuristic Routing and Wavelength Assignment (RWA) algorithms named Least Count First (LCF) and Least Recently Used First (LRUF) for light-path routing in optical WDM networks under dynamic traffic conditions to meet wavelength continuity constraint. The performance analysis of these two algorithms has been simulated to compare the findings with the existing Fixed Order (FO) algorithm. The analysis reports a significant improvement for the proposed algorithms over the FO algorithm in terms of connection requests handling capability, as the former needs less wavelength scans to satisfy a connection request. [ABSTRACT FROM AUTHOR]

Bandwidth required to transmit a signal or bandwidth of a transmission media plays an important role in any form of communication (wired or wireless). This paper explains the importance of bandwidth and how we can choose modulation technique, multiple access technique and other parameters for broadband communication so that the available bandwidth gets enhanced. The paper compares the majorly used analog to digital encoding technique Delta Modulation (DM) with Pulse Code Modulation (PCM) in terms of required bandwidth for number of users (channels). It was found that DM is better. The probability of error is an important parameter to fix channel capacity. In the analysis, it was found that probability of error for Binary Phase Shift Keying (BPSK) and Orthogonal Frequency-Division Multiplexing (OFDM) is better than Quadrature Phase Shift Keying (QPSK) and Direct Sequence (DS)-Code Division Multiple Access (CDMA) respectively. We can efficiently utilize bandwidth by selecting bandwidth-efficient analog to digital encoding methods like DM and BPSK as modulation techniques, and OFDM-CDMA as multiple access technique with digital equipments. [ABSTRACT FROM AUTHOR]

The paper proposes a Medium Access Control (MAC)-protocol for medium-size-Ad Hoc networks. The protocol supports quality-of-service over several hops by reservation of time slots. As a new feature, the protocol avoids the hidden and exposed terminal problem by a two-hop reservation, not by the RTS/CTS protocol. [ABSTRACT FROM AUTHOR]

This paper presents a novel design of Complementary-Symmetry rectangular Microstrip Antenna (CSMA) with modified ground plane for compactness, enhanced gain, bandwidth and low cross-polarization operation. A 58% size compactness is achieved when compared with the conventional rectangular microstrip antenna. The antenna operates for 18.78% of bandwidth and gives maximum of 8.21 dB gain. The cross-polar power level of --22.9 dB down is obtained with respect to co-polar. The effect of complementary-symmetry geometry and modified ground plane for improving the antenna parameters is studied and reported. The experimental results are in agreement with the simulated results. The proposed antennas may find applications in wireless communication systems. [ABSTRACT FROM AUTHOR]

Multi-Input Multi-Output (MIMO) systems with multiple antennas at both the transmitter and receiver are anticipated to be widely employed in future wireless networks due to their predicted tremendous system capacity. Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier modulation technique which takes the benefits of high spectral efficiency, resiliency to RF interference, and lower multi-path distortion. The combination of MIMO-OFDM is very natural and beneficial since OFDM enables support of more antennas and larger bandwidths. To protect the transmitted data against random channel impairments, it is desirable to employ Link Adaptation (LA). To perform LA, the transmitter should know the prevailing channel state information. Generally, the Signal-to-Noise Ratio (SNR) is used as a Channel Quality Indicator (CQI) but in complex MIMO-OFDM systems, this is not sufficient. Therefore, more advanced channel quality indicators such as instantaneous SNR, Shannon capacity and Log Likelihood Ratio (LLR) values are to be considered for efficient link adaptation. The main objective of this paper is to estimate the channel information using LS and QR Decomposition (QRD) algorithm. And also to enhance the performance of the multiuser MIMO-OFDM system in terms of quality and capacity using an efficient link adaptation technique mechanism. The obtained simulation results also prove that the quality of the system is highly enhanced by using channel estimation algorithms. [ABSTRACT FROM AUTHOR]

A new type of Multi-Slotted Patch Antenna with Stripline Fed (MSPASF) is designed and analyzed using IE3D electromagnetic simulation software. Dual wide band characteristics with better Return Loss (RL) up to -20 dB are obtained having gain of 6.1 dBi. The impedance bandwidth of MSPASF is enhanced from 2% (for conventional antenna) to 28.3% by novel slots on the patch plane. Designed antenna finds its applications in wireless frequency band such as fixed satellite services, satellite-based applications, radar, etc. The design procedure and results such as RL, radiation pattern, gain, directivity and current distribution are presented and discussed. [ABSTRACT FROM AUTHOR]

In bandwidth-efficient digital transmission, the training of a receiver requires a start-up process. This start-up includes three steps of setting the automatic gain control, recovering timing and converging the adaptive filters. For many applications, some predefined set of bits are sent to the receiver periodically known as training sequence, which can be used as an ideal reference by the receiver because it is already known to receiving side. Such system is called supervised or trained. However, sometimes the use of training sequence, is not feasible or not desirable. In such case, blind equalization is used which is invariably adaptive in nature. Blind equalization requires less channel bandwidth, but it poses some challenges and also increases system complexity. The most challenging aspect of blind equalization is the convergence of the adaptive equalizer. Without ideal reference, the receiver has to make decisions about what data have been transmitted. Generally, we use a decision device to make assumptions on the input signal. This decision device is called slicer. The decisions are highly unreliable because the received data are corrupted by Intersymbol Interference (ISI) due to distortion introduced by communication channel. As a result, the equalizer does not converge with Least Mean Square (LMS) algorithm because the probability of wrong decision is too high. Several algorithms were developed in the past for blind equalization. The most common are the Constant Modulus Algorithm (CMA) and Reduced Constellation Algorithm (RCA). Both algorithms have been successfully used in many practical applications in data communications. [ABSTRACT FROM AUTHOR]