Khaizuran Abdullah

Bio: Khaizuran Abdullah is an academic researcher from International Islamic University Malaysia. The author has contributed to research in topics: Wavelet & Antenna (radio). The author has an hindex of 8, co-authored 90 publications receiving 403 citations. Previous affiliations of Khaizuran Abdullah include RMIT University & Neelain University.

Studies on DWT-OFDM and FFT-OFDM systems

Abstract: Comparative studies on DWT-OFDM and FFTOFDM systems are presented The model for DWT-OFDM includes zero-padding and vector transpose for transmitting the OFDM signal MATLAB simulation commands are also described The discrete wavelet transform-OFDM (DWT-OFDM) has to satisfy the orthonormal bases and the perfect reconstruction properties to be considered as wavelet transform Different wavelet families have been used and compared with the conventional FFT-OFDM system It is found that the DWTOFDM platform has less mean amplitude for transmitting the signal as compared to conventional FFT-OFDM system Results also show that DWT-OFDM is superior as compared to FFTOFDM with regards to the bit error rate (BER) performance, especially when it uses bior55 or rbior33 wavelet family

Performance of Fourier-based and wavelet-based OFDM for DVB-T systems

Abstract: We present a comparative study on Fourier-based OFDM (FFT-OFDM) and wavelet-based OFDM (DWT-OFDM) in DVB-T system (DWT being the discrete wavelet transform).We found that the DWT-OFDM outperforms FFT-OFDM in AWGN and Rayleigh fading channels. For AWGN channel, the gain in term of energy per bit to noise ratio Eb/No was improved by about 5 dB when the system used Haar wavelet compared to FFT-OFDM with a cyclic prefix (CP) of 1/4-th the total OFDM symbol period, for the same BER of 0.001. Other members of Daubechies families such as db8, db16 and db32 also outperformed by the gains of 7 dB, 10 dB and 11 dB, respectively, at the same BER. We also considered Daubechies wavelet db32 and FFT-OFDM with a CP of 1/4-th the total OFDM symbol period in the presence of narrowband interference. In terms of Eb/No, DWT-OFDM surpassed FFT-OFDM by 9 dB at 0.02 BER. It is also shown that the DWT-OFDM of Daubechies db8 and db1 outperform FFT-OFDM in Rayleigh fading, both in multipath flat fading and multipath frequency selective fading. The DWT-OFDMpsilas with db8 and Haar outperformed FFT-OFDM by 7 and 2 dB, respectively, at BER of 0.01 in the flat fading channel. In addition, DWT-OFDM and FFT-OFDM showed about the same performance below 10 dB of Eb/No in frequency selective fading. However, the wavelet-based OFDM showed significant improvement of performance at higher than 10 dB of Eb/No.

Modification of Distance Factor in Rain Attenuation Prediction for Short-Range Millimeter-Wave Links

Abstract: Prediction accuracy of rain attenuation on short-range millimeter-wave (mm-wave) terrestrial links is of the utmost importance for signal strength prediction and link budget of 5G systems and beyond. This letter contributes to the prediction of rain attenuation over millimeter-wave frequencies for a short-range path (less than 1 km). Interestingly, rain-induced attenuation predicted by utilizing ITU-R P.530-17 largely overestimates the measured data at 26 and 38 GHz with 300 m path length in Malaysia. This is due to the inclusion of the distance factor, which ranges between 2.5 ( f = 38 GHz) and 2.54 (26 GHz). The behavior of the distance factor is investigated thoroughly, and it is found that the maximum values of the distance factor are inconsistent for the path lengths less than 1 km. Consequently, a modification for the distance factor r in ITU-R P530.17 has been proposed. The rain attenuation data measured are utilized to validate and improve the proposed modifications. In addition, available rain attenuation measurements at 25 GHz for 223 m path length in Japan and 75 GHz for 10 m path length in Korea are also utilized for validation. Subsequently, several available measurements from different locations are used to validate the accuracy of the proposed model and are found in good agreement.

Inter-cell interference coordination in LTE-A HetNets: A survey on self organizing approaches

Abstract: Heterogeneous Networks (HetNet) are multi-mode, multi-layer, and multi-band structured and utilize cells of varying sizes. The goal behind the implementation of HetNets involves incrementing the capacity of the established network, modifying spectrum use, lowering the capital and operating costs, and offering steady user-based experience of network architecture. However, these random small cell deployments cause severe problems and results interference in the network. Therefore, the ultimate is the total system performance degradation and this interference becomes a key challenge in HetNet. This article investigates the performances of the current trends and approaches of interference in self organizingnetwork for LTE-A.

On the DWT- and WPT-OFDM versus FFT-OFDM

Abstract: We demonstrate simulation approaches for wavelet based OFDM, particularly in DWT and WPT-OFDM as alternative substitutions for Fourier based OFDM. We begin by constructing the models of the inverse and forward transforms, which can be flexible for substitutions in an OFDM system. We explain in detail each model and study the BER performance. The wavelet based OFDM (DWT-OFDM and WPT-OFDM) is assumed to have orthonormal bases properties and satisfy the perfect reconstruction property. We use different wavelet families and compare with conventional FFT-OFDM system. We found that the DWT-OFDM platform is superior as compared to others as it has less error rate, especially when it uses bior5.5 or rbior3.3 wavelet family.

Always Best Connected

Abstract: This chapter contains sections titled: Product Definition for Broadband Wireless Systems Technology Drivers Evolving Wireless Broadband Market Segments Open Systems and Intelligence at the Edge Radio Network System Engineering References

Millimeter wave beamforming for wireless backhaul and access in small cell networks and practical approaches in software-defined radio

Abstract: Mobile data traffic will continue its tremendous growth in some markets, and has already resulted in an apparent radio spectrum scarcity. There is a strong need for more efficient methods to use spectrum resources, leading to extensive research on increasing spectrum reusability on flexible radio platforms. This study solves this problem in two sub topics, millimeter wave communication on wireless backhaul for spectrum reusability, and flexible prototyping radio platform using software-defined radio (SDR). Wireless backhaul has received significant attention as a key technology affecting the development of future wireless cellular networks because it helps to easily deploy many small size cells, an essential part of a high capacity system. Millimeter wave is considered a possible candidate for cost-effective wireless backhaul. In the outdoor deployment using a millimeter wave, beamforming methods are key techniques to establish wireless links in the 60 GHz to 80 GHz to overcome pathloss constraints (i.e., rainfall effect and oxygen absorption). The millimeter wave communication system cannot directly access the channel knowledge. To overcome this, a beamforming method based on codebook search is considered. The millimeter wave communication cannot access channel knowledge, therefore alternatively a beamforming method based on a codebook search is considered. In the first part, we propose an efficient beam alignment technique using adaptive subspace sampling and hierarchical beam codebooks. A wind sway analysis is presented to establish a notion of beam coherence time. This highlights a previously unexplored tradeoff between array size and wind-induced movement. Generally, it is not possible to use larger arrays without risking a performance loss from wind-induced beam misalignment. The performance of the proposed alignment technique is analyzed and compared with other search and alignment methods. Results show significant performance improvement with reduced search time. In the second part of this study, SDR is discussed as an approach toward flexible wireless communication systems. Most layers of SDR are implemented by software. Therefore, only a software change is needed to transform the type of radio system. The translation of the signal processing into software performed by a regular computer opens up a huge number of possibilities at a reasonable price and effort. SDR systems are widely used to build prototypes, saving time and money. In this project, a robust wireless communication system in high interference environment was developed. For the physical layer (PHY) of the system, we implemented a channel sub-bandding method that utilizes frequency division multiplexing to avoid interference. Then, to overcome a further interfered channel, Direct Spread Spectrum System (DSSS) was considered and implemented. These prototyped testbeds were evaluated for system performance in the interference environment.

Real Measurement Study for Rain Rate and Rain Attenuation Conducted Over 26 GHz Microwave 5G Link System in Malaysia

Abstract: In this paper, real measurements were conducted to investigate the impact of rain on the propagation of millimeter waves at 26 GHz. The measurements were accomplished using a microwave fifth generation radio link system with 1.3 km path length implemented at Universiti Teknologi Malaysia Johor Bahru, Malaysia. The implemented system consisted of Ericsson CN500 mini E-link, radio unit, rain gauge, and data logger. The measurements were attained and logged daily for a continuous year, with 1-min time intervals. Next, the MATLAB software was used to process and analyze the annual rain rate and rain attenuation, including for the worst month. From the analyzed results, it was found that at 0.01% percentage of time, the rain rate was 120 mm/hr; while the specific rain attenuation was 26.2 dB/km and the total rain attenuation over 1.3 km was 34 dB. In addition, the statistics acquired from the measurements for the worst month were lower than what was predicted by the international telecommunication union (ITU) model; around 51% and 34% for the rain rate and rain attenuation, respectively. The average percentage of error calculated between the measurements and predicted results for the rain rate and rain attenuation were 143% and 159%, respectively. Thus, it can be concluded that the statistics for the worst month in Malaysia is lower than what was predicted by the ITU model.

OFDM for Optical Communications

Abstract: Orthogonal frequency division multiplexing (OFDM) is a modulation technique which is now used in most new and emerging broadband wired and wireless communication systems because it is an effective solution to intersymbol interference caused by a dispersive channel. Very recently a number of researchers have shown that OFDM is also a promising technology for optical communications. This paper gives a tutorial overview of OFDM highlighting the aspects that are likely to be important in optical applications. To achieve good performance in optical systems OFDM must be adapted in various ways. The constraints imposed by single mode optical fiber, multimode optical fiber and optical wireless are discussed and the new forms of optical OFDM which have been developed are outlined. The main drawbacks of OFDM are its high peak to average power ratio and its sensitivity to phase noise and frequency offset. The impairments that these cause are described and their implications for optical systems discussed.