Feroz Ahmed

Multiwavelength erbium-doped fiber Fabry-Pe/spl acute/rot laser and its uniform spectral lines power operation

Multiwavelength erbium-doped fiber laser by means of phase modulation in a linear cavity configuration is presented. Stable multiwavelength lasing is achieved by applying any one of the waveforms of sine, square, sawtoothed, and triangular at a suitable frequency between 500 Hz to a few tens of kilohertz to the phase modulator. The output spectral lines power equalization is performed by adjusting the frequency to drive the all-fiber phase modulator and the polarization controller or dc offset voltage of a LiNbO/sub 3/ amplitude modulator, which is incorporated in a polarization-maintaining fiber Lyot-Sagnac filter.

Comparative study of rectangular and circular microstrip patch antennas in X band

A comparative performance study of rectangular and circular shape microstrip patch antennas at an X band frequency is presented in this paper. The resonant frequency is chosen at 10 GHz which is suitable for a variety of wireless applications. CST Microwave Studio is used as the software environment to design and compare the performance of the antennas. It is found that the rectangular patch antenna shows about 3.0 dB higher return loss than the return loss of circular patch antenna. In addition, the rectangular patch antenna has an improved VSWR value of 1.18 than that of the circular patch with VSWR 1.27. However, circular patch antenna offers about 8% higher bandwidth and nearly 2.0dB less side lobe power than that of rectangular patch antenna.

Application of acoustic sensing and signal processing for PD detection in GIS

The presence of free moving metallic particles and discharges deteriorates the insulation strength of a compressed SF/sub 6/ (sulphur-hexafluoride) gas insulated switchgear (GIS) and causes serious limitation in its practical application. Free moving metallic particles and other defects inside the GIS cause partial discharge (PD) which can degrade the insulating properties of the insulant gas SF/sub 6/ to such an extent that breakdown may occur in the GIS system. So, it is necessary to detect partial discharge in the GIS at an early stage before system failure and extensive damage to the equipment and the rest of the power system. Partial discharge emits acoustic signals which can be detected by applying an acoustic emission sensor (AE sensor) outside the GIS chamber. This paper initially describes some fundamental aspects related to PD detection. Finally, the development of an acoustic PD detection system and some experimental investigations are presented.

Numerical Modeling and Experimental Confirmation of an Efficient Phosphosilicate-Fiber Raman Laser

A model for a fiber Raman laser has been numerically solved including all the interactions between forward and backward travelling waves. The predicted numerical results are experimentally confirmed using a fiber Raman laser with P2O5-doped fiber. The maximum output power of 3.1 W at 1483.5 nm with a slope efficiency of 46% is experimentally obtained using a 300 m P2O5-doped fiber. Numerical results suggest that an output power of as much as 4 W with a slope efficiency of 57% can be achieved if the Raman cavity is optimized for the same input pump power.

An efficient anti-collision technique for Radio Frequency Identification Systems

Collision is a problem which degrades the performance of the radio frequency identification (RFID) system while multiple tags are communicating with the reader simultaneously. Currently this problem is handled by various procedures such as framed ALOHA protocol, binary tree protocol, tree walking algorithm or using spread spectrum modulation scheme. The current solutions are slow, power wasting and cannot solve collision problem in better aspect. The proposed system eliminates collision while multiple tags are responding to the reader under its network and provides better power savings than existing systems.

SIP-Based QoS in IP Telephony

In this paper, the authors analyze the factors resulting to the degradation of the quality of service in voice over IP (VoIP) telephony. SIP protocol is used to explore the QoS characteristics of different Codec. The system is designed for an IP telephony service provider with other GSM operator network cloud. A soft IP PBX maintains the dial pattern, SIP proxies are used in order to implement call control and to allow the distributing of the gateways’ lines. The system is executed in a test bed where QoS factors likes delay, packet loss, forward and reverse jitter, MOS and delta measured. A Popular simulation software Wireshark is used to simulate and analysis the transmission characteristics of packetized voice over the IP network channel. The results are graphically shown, which reveal the effects of packet size on QoS. Packet sizes from 10 to 60 bytes are used for a G.729 Codec in 11.2-24 Kbps channel bandwidths are studied. A 20 byte packet size at 24 Kbps channel bandwidth is seen to show the best result in terms of jitter, delay and delta. The results of studies conducted by also shown that G.729 codec shown high MOS value and low mean forward and reverse jitter for simultaneous call compare with other codecs

Adaptive Companding as a PAPR Reduction Technique of an OFDM Signal

In this paper, a new adaptive PAPR reduction scheme is proposed by which the PAPR of the OFDM signal can be reduced to keep the value lower than a predefined threshold level. A conventional companding is used as a technique to reduce the PAPR of the OFDM signal. If the PAPR of the OFDM signal is higher than any predefined level, one or more times companding operations are performed until the PAPR becomes lower than that level. On top of that, no companding is applied if the signal’s PAPR is lower than the predefined level. However, there is a trade-off between the improvement of the PAPR and BER which may be optimized based on any specific application requirements

Defect detection and identification of sources in GIS based on laboratory and on-site experience

The most common defects in GIS apparatus are due to the presence of metallic particles, protrusions, as well as floating shields which originate mainly from imperfect manufacturing process, operation of switches, or may become trapped during assemble. The presence of defects deteriorates the insulation strength of a compressed SF/sub 6/ GIS apparatus and causes serious limitation in its practical application. These defects can be detected by several techniques, one of which is that using acoustic sensors placed on the enclosure. This paper reports on the defect detection and identification of sources in GIS apparatus using acoustic technique, based on laboratory and on-site experience. The tests give satisfactory result.

An activating framework using software defined radio to enhance classroom teaching for wireless communication courses in developing countries

In the modern era of technological revolution, it has become essential for the developing countries to develop their technological capability. This urges for the enhancements in all aspects of education including engineering. Enhancement of the learning experience for the students, by the incorporation of experimentation in classroom teaching is one of the potential methods to do that. This paper proposes a system for enhancement of the classroom teaching of telecommunication engineering courses by the incorporation of experimentation demonstration with the theoretical concepts using a remotely accessed Software Defined Radio based system. This will allow the faculty members to combine the practical results with the complicated communication theories to provide the students with better learning environment. Also this immediate and tangible experience will benefit the students in applying the complex theoretical concepts that they are trying to capture. Two examples of possible innovative classroom demonstrations of system developed with software defined radio are presented in this paper. To support the demonstration of the proposed system, a remotely accessed SDR based low cost experimentation setup has been designed and developed, details of which is also presented here.

Channel-Spacing Tunable and Multiwavelength Switchable Erbium-Doped Fiber Laser

Channel-spacing tunable and multi-wavelength switchable EDFL based on a single-segmented PMF Lyot-Sagnac filter and phase modulator is presented. The tuning and switching are performed by means of a polarizer and PC, respectively; those are incorporated in the filter.