Razali Ngah

Development of a New Approach for High-Quality Quadrupling Frequency Optical Millimeter-Wave Signal Generation Without Optical Filter

In this paper, we propose a new approach to generate quadrupling-frequency optical millimeter-wave (mm-wave) signal with carrier suppression by using two parallel Mach-Zehnder modulators (MZMs) in Radio-over-flber (RoF) system. Among the numerous properties of this approach, the most important is that a fllterless optical mm-wave at 60GHz with an optical sideband suppression ratio (OSSR) as high as 40dB can be obtained when the extinction ratio of the MZM is 25dB. Simplicity and cost-efiectiveness have made this approach a compelling candidate for future wave-division-multiplexing RoF systems. Theoretical analysis is conducted to suppress the undesired optical sidebands for the high-quality generation of frequency quadrupling mm-wave signal. The simulation results show that a 60GHz mm-wave is generated from a 15GHz radio frequency (RF) oscillator with an OSSR as high as 40dB and an radio frequency spurious suppression ratio (RFSSR) exceeding 35dB without any optical or electrical fllter when the extinction ratio of the MZM is 25dB. Furthermore, the efiect of the non-ideal RF-driven voltage as well as the phase difierence of RF-driven signals applied to the two MZMs on OSSR and RFSSR is discussed and analyzed. Finally, we

Various Slotted UWB Antenna Design

This paper presents various slotted antenna. The proposed antenna is designed in order to meet Ultra Wideband (UWB) requirements and applications. This antenna has small in size enabling it to be fixed into Wireless Personal Area Network (WPAN) devices. There are three types of proposed slotted antennas; T slotted for patch and feeding strip, couple a ring and L slots, and dual asymmetry L slots. From the simulation results, matching bandwidth is due to the shape of the antenna close to the feeding point, where currents are the strongest. It is shown that to better control an antenna behavior, it is necessary to observe the current distributions which give most contribution on matching performance. The T slot on the feeding strip produces more vertical current thus improve the matching impedance performance at higher frequencies, the ring slot with the open angle of 90o and radius (r1) of 3 mm has shown an improvement to the return loss at the lower resonance of 5 GHz and the upper resonance of 10 GHz, the dual asymmetry L slot on rectangular patch has shown multiple resonances. Their simulated return loss and radiation pattern meet the UWB requirements. The slot types are as novelty for this work.

Simulation of an all optical time division multiplexing router employing symmetric Mach-Zehnder (SMZ)

Synchronisation is an important and critical issue in high-speed all optical time division multiplexed (OTDM) packet routing and transmission. In this paper we present a technique for separating the clock synchronization pulse from an incoming optical time division multiplexed data packet, based on all-optical switching devices with optical feedback. A 1/spl times/2 OTDM router composed of three symmetric Mach-Zehnders (SMZs) is proposed. Simulation results show that synchronization between clock and data packet is achievable and the packet payload can be successfully switched to the correct destination port.

Representation of antenna in two-port network s-parameter

Antenna return loss and gain as function of frequency are not readily accommodated in many communication system software. This paper proposes solution to the problem by representing the antenna in two-port network s-parameter. The representation exploits the analogy between antenna and two port network. Simulation using communication system software shows that the proposed method is validated.

Modelling of all-optical symmetric Mach-Zehnder switch with asymmetric coupler

Ultra high-speed optical network is developing rapidly as growing capacity demand in telecommunication system is increasing. In these networks, it is desired to carry out switching, routing and processing in optical domain to avoid bottlenecks of optoelectronic conversions. Optical time-division multiplexing (OTDM) technique is one option to implement all optical networks. It provides a single data stream at a very high rate (>100 Gbits/s) using a single wavelength. These networks will be based on optical packet switching. The success of these networks depends on how well switching and routing are being done at this very high speed. An all optical switch based on symmetric Mach-Zehnder (SMZ) with asymmetric coupler (60:40) is proposed. Its characteristics and switching window profiles will be investigated. The results show that symmetric Mach-Zehnder (SMZ) with asymmetric coupler gives a better contrast ratio rather than symmetric Mach-Zehnder (SMZ) with normal 50:50 coupler.

Study the performance of OFDM radio over fiber for wireless communication systems

Radio-over-fiber (ROF) technology has several advantages such as providing huge bandwidth, inherent immunity to electromagnetic interference and reduced power consumption. This paper presents a simulation to investigate the performance of orthogonal frequency division multiplexing (OFDM) as a modulation technique to transmit the basebands signal over fiber. The model contains a laser diode used as optical modulator to convert the signal from baseband to optical frequency. The QPSK-OFDM transmitted signal and power spectrum are obtained for both of AWGN and optical fiber link channels. The study reveals that the OFDM performance on the optical fiber link in terms of spectrum containment is nearly similar to that on AWGN channel. The significance of this study comes from the promising future of using optical fibers to transmit radio signal. Consequently the model of this paper can be used with different wireless communication systems such as wireless LANs and digital video broadcasting (DVB) and it is supporting to the 4th generation cellular systems. The details of design and simulated results for the proposed model are presented and discussed.

5.8 GHz photonic antenna for point to point applications

Due to its low propagation loss, large bandwidth, and competitive cost, optical fiber become one of the best solution for the backhaul. However, new fiber network deployment is still very expensive in outdoor and rural environment. This paper proposes and evaluates design of 5.8 GHz photonic antenna in a radio over fiber system for point-to-point applications. Simulation result shows that the proposed system can support 540 Mbps, 16-QAM, at 5.8 GHz for optical fiber length of 30 km, and extended with wireless distance of 10 km.

Wavelet-domain channel characterization for mobile broadband communication systems

Channel characterization and state information play important role in the realization of optimal performance in communication systems. In mobile communication systems, the channel is realistically nonstationary and is often modeled equivalently as time-frequency integral operator with finite supports in time and frequency, employing the Fourier kernel and fixed window as the analyzing functions which result in poor time-frequency resolution and is unsuitable for representation of nonstationary systems. And as such this form of characterization is not adequate in accurately tracking channel variations especially in fast fading and frequency selective channels. In this paper, we present a method of mobile radio channel characterization and description in the wavelet-domain which promises a better joint time-frequency variations representation assuming nonstationary channel condition and very suitable for mobile broadband communication system.

Optical generation of 60-GHz signal for millimeter wave wireless communication

In this paper, a quadruple-frequency optical millimeter-wave (mmW) signal generation using an integrated dual-parallel MZM (IDP-MZM) is presented. With properly adjusting the phase delay, biasing, and modulation index, an optical mmW signal at 60-GHz with an Optical Sideband Suppression Ratio (OSSR) up to 28 dB is obtained through simulation. The Radio Frequency Spurious Suppression Ratio (RFSSRR) is 32.2 dB. Furthermore, the impact of non-ideal MZM on RFSSRR is studied through simulation. Although a large modulation index is utilised to achieve frequency quadrupling, the simplicity and high quality have made this scheme a viable solution for mmW wireless communication networks.

Stationarity Regions for Ultrawideband Channels

In this letter, extracting the stationarity regions (SRs), where the channel statistics changes are insignificant, for ultrawideband (UWB) channel is achieved. SRs are found based on the correlation between consecutive power delay profiles (PDPs). The PDPs are found from channel measurement data for a frequency range of 3.1-5.3 GHz. The measured channel exhibits the sparsity behavior. Results show that the obtained SRs are between 0.27-0.32 m, where short distances show the variability of the channel. Moreover, the results are compared to standard probability density functions (PDFs). The generalized extreme value, Weibull, and exponential distributions are seen as the best fitted PDFs.