nan Iskandar

Prediction of Propagation Path Loss for Stratospheric Platforms Mobile Communications in Urban Site LOS/NLOS Environment

Recently, there are of great interests on employing stratospheric platform as a new means of providing IMT-2000. One important issue that has not been much investigated is the propagation characteristic of its link. This paper aims at evaluating the impact of elevation and azimuth angles variation to the propagation mechanism in urban environment for mobile communication link. In order to examine the propagation loss experienced by this system in urban area, we developed the building block model and the ray tracing tool for simulation. We then apply the ray tracing tool with respect to the angle variations. As a result, propagation loss as a function of elevation and azimuth angles is obtained. We compared the result with a physical-statistical model for verification. Finally, link budget analysis and estimation to the required transmitted power at several transmission rates for the application of IMT-2000 is observed. Different scenario, which means different azimuth angles clearly show the critical limitations for mobile communication using a concept of stratospheric platform.

WLCp2-11: On the Downlink Performance of Stratospheric Platform Mobile Communications Channel

This paper considers the downlink performance of mobile communication channel based on a novel wireless infrastructure that is called stratospheric platforms (SPF). The SPF has been recently proposed as an alternative method for delivering mobile communication services such as IMT -2000 in parallel with cellular tower-based terrestrial system or satellite. Channel performance evaluation is now becoming a matter of urgency in the designing of communication link between the platform and mobile user. We first evaluate propagation characteristic in urban area in order to obtain propagation parameters in terms of path loss model and Rice factor. Due to their unique positioning, elevation and azimuth angle are considered as main parameter in SPF environment compared with terrestrial tower-based system. The propagation parameters are then used in order to evaluate downlink performance for IMT -2000 services served by the SPF. Different applications refer to different information bit rate that is carried by IMT -2000 system are considered in the analysis. In all scenarios, downlink performance decreases as the service bit rate increases and it becomes worse when elevation angle lower than 40deg.

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.

Performance Evaluation of Broadband WiMAX Services over High Altitude Platforms (HAPs) Communication Channel

First, this paper describes a prediction of Rice factor (K factor) estimation for a high altitude platforms (HAPs) wireless channel. Estimation is based on experimental data which was collected from an object floating above the ground and carrying transmitter apparatus to perform as a HAPs. This experiment is intended to study multipath channel behaviour represented by K value for a wireless communication using HAPs. We use moment-based method estimator to characterize HAPs-channel in a wide interval of elevation angle. Secondly, the performance of WiMAX (IEEE802.16e) high speed transmission is simulated over the predicted HAPs channel. It is also shown how Doppler effect and K factor which is governed by elevation angle can contribute to the performance. We found that WiMAX services, which require high level requirement, fail to achieve an acceptable performance over HAPs channel if the elevation angle is lower than 40 degrees.

Analysis of CDMA Capacity for Multiple Stratospheric Platform Mobile Communications under Imperfect Power Control and Fading

We propose an analysis of CDMA multispot beam for reverse link multiple stratospheric platforms (SPF). Evaluation on the CDMA system capacity of this technology has not been much reported especially for multiple SPF scenarios. This paper addresses all possible multiple access interference including the effects of channel fading and shadowing in order to evaluate the system capacity. The analysis is based on perfect power control and imperfect power control. The results indicate that in SPF systems the reverse link CDMA capacity is significantly reduced because of the power control imperfections. In multiple SPF model the interference caused by the users in overlapped region is not trivial. Because of this problem the capacity is reduced for both speech and real-time data applications even though the assumption of perfect power control can be made.

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.

Pilot-based estimation for SC-FDMA LTE in high altitude platforms (HAPS) channel

This paper aims at evaluating pilot-based estimation technique for SC-FDMA LTE deployed via high altitude platforms (HAPS) channel. HAPS is a novel wireless infrastructure in which one of its applications is to carry cellular system such as 4G LTE. The problem of SC-FDMA LTE signal transmission over HAPS channel is due to multipath from objects nearby the mobile user. Signal at the receiver, which in this case receiver is an eNB onboard the platform, will be suffering from fluctuation due to fading. Since the channel conditions fluctuate, immediate channel state information (CSI) needs to be estimated in a short time. Pilot signal or a so-called training sequence is a popular approach to estimate CSI. HAPS channel is known to follow Ricean fading distribution. In our work, pilot-based estimation is evaluated under HAPS Ricean channel. The channel variation is governed by users elevation angle. Modulation type and LTE channel bandwidth are also investigated.

Effect of HAPS movement on the performance of downlink power control CDMA system

Power control is a mandatory method in CDMA based system, including in high altitude platform station (HAPS) WCDMA system evaluated in this paper. HAPS is a new means of wireless delivery method located at stratospheric layer and act as the base station providing the communication systems. Platform located at that layer will be affected by the wind. Therefore, the platform is supposed to move from original position and then experience an instability condition. In this paper, this practical situation of HAPS will be evaluated in term of the power control performance. We evaluate two distance-based power control schemes for the downlink HAPS channel. The first scheme is an optimum power control and the second scheme is nth power of distance power control. Computer simulation shows that the performance of distance-based power control scheme is significantly affected by the movement of HAPS.

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.

Step Size Optimization for Fixed Step Closed Loop Power Control on WCDMA High Altitude Platforms (HAPs) Channel

This paper evaluates fixed step algorithm of closed loop power control and investigates an optimum step size for WCDMA communication employing high altitude platforms (HAPs). In CDMA, power control must be used to overcome near-far effect, shadowing and multipath fading. Users who are distributed within HAPs coverage will have different channel characteristic depending on their elevation angle. Therefore, parameter of power control algorithm should be designed to comply with the channel characteristic. Step size is one parameter in fixed step closed loop power control that will be investigated in this paper. Considering the measured HAPs channel characteristic, this paper investigates an optimum step size that will resulting a minimum power control error (PCE). Computer simulation shows that optimum step size depends on users elevation angle. The higher the elevation angles the smaller the optimum step size of the power control.