Khaizuran Abdullah

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

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.

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

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.

Empirical conversion of rainfall rate distribution for various integration times in Malaysia

The study of rainfall rate integration time is important to designers of satellite communication systems. In most part of the world, long-term rain statistics are typically available for integration time of very long durations; even perhaps of one hour or more. The method and appropriate conversion of rainfall rate distribution from variable integration times to the equivalent 1-minute are indeed vital. This is due to the fact that established prediction methods for estimating the rain induced attenuation on satellite-Earth links utilize the 1-minute rainfall rate data.

Rain fade characteristics analyses for V-band link in tropical region

A decade ago, the operating frequencies of most available satellites in the tropics were C band, S-band and Ku-band. The V-band satellite links were initially confined mainly to temperate regions. Recently however, this new service has gradually been introduced worldwide including the tropical regions. In the future, new satellites in the tropical and equatorial will also have no alternative but to operate at V-band and higher frequencies due to spectrum limitations. Therefore, it is very critical to be able to predict accurately the likely impairment to be encountered on a given link in order to plan the services economically. The predicted value of signal loss and fading are used to determine the design parameters. This paper aimed to discuss the seasonal, diurnal and possible fade mitigation technique that can be used and the challenges to be able to use V-band frequency in tropical region in the future.

A modified rain attenuation prediction model for tropical V-band satellite earth link

Radio wave propagation plays a very important part in the design and eventually dictates performance of space communication systems. Over time, the requirements of satellite communication have grown extensively where higher capacity communications systems are needed. Escalating demands of microwave and millimetre wave communications are causing frequency spectrum congestion. Hence, existing and future satellite system operators are planning to employ frequency bands well above 10 GHz. The challenge in operating at such high frequencies for communication purposes is that there exists stronger electromagnetic interaction between the radio signals and atmospheric hydrometeors. Such instances will degrade the performance of such high frequency satellite communication systems. The development of a revised model for a better-improved rain fade prediction of signal propagations in tropical region is considered very important. Researchers and engineers can employ the model to accurately plan the future high frequencies satellite services.

Performance analysis of two component carrier selection algorithms in the downlink LTE-A

This paper studies the performance of two well-known Component Carrier (CC) selection algorithms in static and dynamic allocation so as to provide satisfactory Quality of Service (QoS) of a Guaranteed Bit Rate (GBR) application. Performance evaluation is conducted using the the downlink Long Term Evolution-Advanced (LTE-A) as the simulation platform. Simulation results demonstrate the efficacy of the Random CC selection algorithm (in dynamic allocation) in optimizing the system capacity without compromising the QoS of the GBR application. However, dynamic allocation comes at the expense of an increase in signalling overhead. Future studies include identification of a new dynamic mechanism for CC selection that can reduce the signalling overhead without compromising the GBR performance.

A study of packet scheduling with mobile cellular channel impairments

Long Term Evolution-Advanced (LTE-A) is a new radio access technology that is expected to provide better experience among the mobile cellular users. It delivers multimedia services using packet switching technology. Therefore, intelligent design of packet scheduling for the LTE-A to provide Quality of Service (QoS) comparable to fixed line services becomes crucial. However, packet scheduling over the LTE-A system faces a number of challenges. This paper studies a number of low complexity real time packet scheduling algorithms developed for the legacy mobile cellular systems. In addition to that, studies on performance impact due to mobile cellular channel impairments are presented. The study aims to identify the methods used by the existing packet scheduling algorithms as well to ascertain the performance degradations on the QoS of multimedia services due to the impact of the mobile cellular channel impairments. Future works include development of a new packet scheduling algorithm to overcome detrimental effects due to LTE-A channel impairments on the QoS of multimedia services.

U-Slot Rectangular Patch Antenna for Dual Band Application

Dual and multi-band rectangular microstrip antennas can be realized by cutting U-slots inside the patch. In this paper, the length and width of U-slots are optimized in order to achieve dual-band and multi-band operation. Computer Simulation Technology (CST) software was used to design, simulate and optimization of antenna. Two resonant frequencies at 1.8 and 2.4 GHz were found with reasonable gain. Additional resonant frequencies could also be achieved from 2.8 to 3.0 GHz using the similar approach.

Inter-cell interference coordination in Heterogeneous Network: A qualitative and quantitative analysis

Heterogeneous Networks (HetNet) comprise networks with specially designed architecture. To cover large areas, established base stations (macro sites) are used; for coating buildings, microcells are employed; for covering individual levels or floors in a building, Pico-cells are utilized; and finally for providing wireless coverage to individual apartments, small offices, and home based businesses, femtocells (HeNodeBs) are exploited. The goal behind the implementation of HetNets involves incrementing the capacity, modifying spectrum use, lowering the capital and operating costs, as well as offering steady user-based experience of network architecture. Furthermore, HeNodeBs have been developed for voice, data, video services in home and offices and a certain outdoor scenario with a very limited geographical coverage. However, these random HeNodeB deployments raises co-tier and cross-tier inter-cell interference which results system performance degradation. The existing approaches have tried to solve Inter-cell Interference (ICI) issues. Yet, these techniques are become unsatisfactory for recent communications as aggressive frequency reuse is desired to maintain high data-rates. In this paper, we investigated and identified recent issues of inter-cell interference coordination problems. The related schemes and techniques are also analyzed in order to highlight the pros and cons of each of the schemes.

Performance evaluation of uncoordinated beamforming over cognitive radio network

This paper presents the two strategies of jointly-optimized uncoordinated beamforming algorithms for cognitive radio networks. Here, we evaluate the performance of signal-to-interference-plus-noise ratio (SINR) and achievable sum rate of the system when both primary and secondary users transmit concurrently over the same spectrum. We present the optimum weight design to maximize the SINR and achievable sum rate for both primary and cognitive link under the condition that the cross interference at both receivers are totally nullified. The interference cancellation is done at the secondary user and no coordination between the primary and secondary users is required as we employed uncoordinated beamforming in the networks. The fairness of the SINR performance in primary and cognitive link when the primary user employing maximal ratio combining beamformer while the secondary user employing discrete search and gradient algorithm is discussed using different number of transmit and receive antennas. Simulation results demonstrate that employing gradient algorithm at the cognitive link is optimum in terms of maximizing SINR and provides a higher rate compared to the discrete search.