Adit Kurniawan

A Modified Bow-Tie Antenna for Improved Pulse Radiation

The analysis, design, and realization of a modified bow-tie antenna optimized for impulse ground penetrating radar (GPR) applications is described. The proposed antenna shows improved properties important for GPR, which include its compact size (in comparison with a conventional bow-tie antenna) and ability to radiate UWB pulses with increased amplitude and very small late-time ringing. A substantial increase in the amplitude of the transmitted pulse is achieved by utilizing radiation from discontinuities introduced by the resistive loading employed in the antenna to suppress late-time ringing. By choosing an optimal distance between the antennas feed point and the location of the resistive loading, radiations that occur from the antennas feed point and the mentioned discontinuities at the resistive loading will combine constructively in the boreside direction of the antenna. As a result, one will observe a substantial increase of the amplitude of the transmitted pulse in the boreside direction. Furthermore, an analytical expression describing approximate time-harmonic current distribution is derived to indicate an optimal resistive loading profile for the proposed antenna. Additionally, the traveling-wave current distribution of the antenna is theoretically analyzed to examine the applicability of the obtained time-harmonic expression for pulse excitation. It has been found that when the antenna is resistively loaded both the time-harmonic and traveling-wave currents decay to approach nearly the same value at the end section of the antenna. As the amount of current at the antenna ends corresponds to the level of reflection which occurs there, the derived expression is found to be useful to indicate an optimal loading profile for the proposed antenna. A theoretical model of the proposed antenna has been developed to perform numerical analysis using a modified NEC-2 code. In addition, an experimental verification has been carried out and both the simulation and experiment confirmed the improved properties of the proposed antenna.

A facility for UWB antenna measurements in time domain

The IRCTR, Delft University of Technology (TU Delft), Netherlands, and the Bandung Institute of Technology (ITB), Indonesia, have been collaborating in a research project on the development of ultra-wideband (UWB) antennas for ground penetrating radar (GPR) applications. In the research, a facility for UWB antenna measurements in the time domain is needed. The paper describes such a facility which has been developed at ITB in the framework of the collaborative project. The UWB antenna measurement facility has been developed based on a technique introduced and implemented by IRCTR (Lestari, A.A., PhD Dissertation, TU Delft, 2003). Additionally, a feature for measuring radiated transient fields using a vector network analyser (VNA) has been included due to the unavailability of time-domain measuring equipment, such as pulse generators and sampling oscilloscope. The measurement facility has been used for measurements of the radiated near fields and input impedance of the UWB GPR antennas developed by IRCTR and ITB (Lestari et al., Proc. 10th Int. Conf. on Ground Penetrating Radar, GPR 2004, vol.1, p.141-4, 2004).

High mobility data pilot based channel estimation for downlink OFDMA system based on IEEE 802.16e standard

High mobility communication systems need suitable channel estimation to cope high frequency selectivity channel effect. In this paper we propose data pilot based channel estimation in downlink OFDMA for IEEE 802.16e standard (mobile WiMAX). The mobile WiMAX channel estimation can be done by exploiting pilot from preamble, in this paper we obtain channel transfer function by exploiting pilot at symbol data with two dimensional interpolation scheme. Based on our simulation, it can be shown that the proposed method have better performance compare with preamble based channel estimation method. Afterwards we compare linear interpolation and MMSE interpolation for proposed channel estimation method. The symbol error rate for QPSK and 64 QAM system is presented by means of simulation.

Multimedia Broadcast Multicast Service over Single Frequency Network (MBSFN) in LTE based Femtocell

Multimedia Broadcast Multicast Services (MBMS) provides a mechanism to support effective delivery of multimedia traffic over cellular network for all users which request the same multimedia data. It was introduced in 3GPP release 6 and has been developed in recent release in term of enhanced MBMS (eMBMS). Current eMBMS can support two kinds of transmission, namely Single-cell transmission (in this mode the MBMS data only can be transmitted inside one single cell coverage) and Multi-cell transmission (in this mode the MBMS data are sent by different cells that are tightly synchronized), which also known as Single Frequency Network (SFN). In SFN all base stations transmit the same signal at the same time and over the same frequency channel to user equipment. In SFN, the transmissions received from multiple cells will, as seen from the UE, appear as a single transmission subject to severe multipath propagation. SFN can bring benefit whichs changes the interference or destructive signal to constructive signal and contain longer cyclic prefix than conventional transmission. Femtocells are low-power wireless access points that operate in licensed spectrum to connect standard mobile devices to a mobile operators network using residential DSL or cable broadband connections. Current Macrocells could support indoor coverage but with some limitations caused by thick walls, high locations and other indoor obstacles. Those were a challenges need to be solved and Femtocells offers more efficient solutions to handle indoor coverage. When first introduced, Femtocells can solved the poor quality of indoor voice and data services. When those problems are solved, more services demanded to be supported by Femtocell, e.g. multimedia services.

Backhaul-aware scheduling for WiMAX femtocell with limited backhaul capacity

A femtocell is designed to use a shared broadband IP link. A bottleneck may be occurred due to the limitation of provisioned bandwidth and the existence of background traffic especially in access network. The bottleneck will certainly affect the service performance of the femtocell access point (FAP), which would influence end user experience. In order to maintain QoS requirement against backhaul quality fluctuation, a FAP should be equipped with a QoS management capability which is aware of backhaul condition. By applying backhaul aware admission control and scheduling, FAP can determine whether or not the backhaul bandwidth capacity is able to support a new service session. FAP will know the backhaul bandwidth by implementing bandwidth estimation. When the congestion occurred, FAP will maintain the existing flows and accept sessions with higher priority services (i.e realtime) over lower priority traffic (ie. non-realtime), based on load demand of each service flows.

Low complexity partial sampled MMSE channel estimation for downlink OFDMA IEEE 802.16e system

Channel estimation is one of key problems in IEEE 802.16e Orthogonal Frequency Division Multiplexing Access (OFDMA) downlink system. Minimum Mean Square Error (MMSE) channel estimation has been known as a superior performance channel estimation. However, this algorithm has high computational complexity. In this paper, we present low complexity partial-sampled MMSE channel estimation for compromising between complexity and performance. We reduced MMSE channel estimation complexity by partially sampling the MMSE weight matrix. The simulation results show that the bit error rate (BER) performance significantly improved over the least square channel estimation and has comparable BER performance with MMSE channel estimation at low SNR. Depending the sixze of sampling, significant decrease 57 % to 64 % in computational complexity can be achieved.

Experiment of slotted triangular triple-band antenna for WiMAX/WLAN application in Indonesia

Based on IEEE 802.11 standard, frequencies of WLAN are: 2.4-2.474 GHz, 5.15-5.35 GHz, 5.475-5.725 GHz, and 5.725-5.825 GHz. Based on WiMAX Forum standard, two major band on certification profile for Fixed WiMAX (band 3.5 GHz and 5.8 GHz) and Mobile WiMAX comprises four frequencies, band 2.3 GHz, 2.5 GHz, 3.3 GHz and 3.5 GHz. At this research, design and implementation of triple-band antenna for WiMAX/WLAN was done. The frequencies of antenna are 2.4 GHz, 3.3 GHz and 5.8 GHz. The design process comprises two steps, simulation and fabrication. A kind of antenna is a microstrip antenna with triangular patch and slotted ground plane. It uses epoxy-FR4 with 1.6 mm of thickness as substrate material. Based on the simulation result by HFSS Ansoft v.11, its get slotted triangular antenna that can works at WLAN and WiMAX frequencies, i.e. 2.4 GHz (2252-2530 MHz), 3.3 GHz (3208-3520 MHz) and 5.8 GHz (5718-5869 MHz). Gains of antenna are 7.88 dB (2.4 GHz), 6.177 dB (3.3 GHz) and 6.89 dB (5.8 GHz). Meanwhile on measurement of antenna as a result of fabrication only one band that is get, 5628-5880 MHz and gain is 6.536 dB. Thats caused by there is a dimension of antenna that is very small (0.005 mm) and cannot be reached by the vendor.

Detection of cerebral aneurysms by using time based parametric color coded of cerebral angiogram

Cerebral aneurysm is a cerebrovascular disorder in which weakening in the walls of brain blood vessels causing a swelling or dilation of blood vessels. The disease is also called intracranial aneurysms and usually occurs around the arteries at the base of the brain called the Circle of Willis.

Performance of Variable Step Closed Loop Power Control in CDMA High Altitude Platforms Communication Channel

This paper evaluates the performance of variable-step closed loop power control algorithm for CDMA communication employing High Altitude Platforms (HAPs). In HAPs, the channel is predicted to have different characteristics compared to that in terrestrial. Users that are distributed within HAPs coverage will have different channel characteristics depending on their elevation angle. In this work, HAPs channel is modeled to follow Ricean fading distribution which K-factor is obtained based on experimental measurements. The variable-step power control algorithm is then computer simulated under such a channel to evaluate its performance. The performance is presented in terms of power control mode (q), user speed, user, elevation angle and power control command error. In many cases, elevation angles have a significant impact to the power control performance, i.e. the performance of the power control is worse at lower elevation angle.

On the evaluation of fixed step closed loop power control for CDMA High Altitude Platforms (HAPs) communication channel

This paper describes the performance evaluation of fixed step closed loop power control algorithm in a novel wireless channel that is called High Altitude Platforms (HAPs). This new wireless delivery method is proposed as a complementary system in providing the next generation services in which the technology basically employs CDMA. In HAPs communication, the channel is predicted to have different characteristic compared to that in terrestrial channel. In this work, HAPs channel is modeled to follow Ricean fading distribution whose K factor is obtained based on experimental measurement. Fixed step power control algorithm is then computer simulated under such a channel to evaluate its performance. The performance is presented in terms of step size of the power control, users elevation angle, feedback delay, and SIR estimation error. We found the performance of fixed step closed loop power control in HAPs channel increases with the increase of step size and elevation angle. Feedback delay has insignificant effect to the power control performance. SIR estimation error degrades the performance of the power control compared with the true SIR estimation.