Mona Riza Mohd Esa

Performance Analysis of MIMO-CDMA System

Nowadays, the demand on communication system is towards high capacity and faster data transmission with minimum error or losses. In wireless communication, multiple input multiple output (MIMO) is one of the techniques that can increase spectral efficiency and link reliability. Therefore, the performance of MIMO-CDMA with comparison to conventional code division multiple access (CDMA) system has been analyzed. The simulations models are simulated with different number of antenna which are two transmit-two receive (2Tx2Rx) and four transmit-four receive (4Tx4Rx). System specification is based on voice application. The simulation results shows that the proposed MIMO-CDMA (2Tx2Rx) is improved by 43% of BER and MIMO-CDMA (4Tx4Rx) improved by 63% of BER performance compared to conventional CDMA. Capacity performance of MIMO-CDMA (2Tx2Rx) improved by 50% and MIMO-CDMA (4Tx4Rx) improved by 75% compared to conventional CDMA

Measurement of bit error rate at 2.4 GHz due to lightning interference

This paper analyzes the interference of lightning flashes with wireless communication systems operating in the microwave band at 2.4 GHz. A bit error rate (BER) measurement method was used to evaluate BER during 3 heavy thunderstorms on January 25, March 17 and March 20, all in year 2011. In addition, BER measurements also were done on January 21 and March 30, 2011 under fair weather (FW) conditions providing a baseline for comparison. The Transmitter-Receiver separation was fixed at 10 meter with line-of-sight (LOS) consideration. We infer that lightning interfered with the transmitted digital pulses which resulted in a higher recorded BER. The maximum recorded BER was 9.9·10-1 and the average recorded BER was 9.95·10-3 during the thunderstorms with the average fair weather BER values under the influence of adjacent channel interference (ACI) and co-channel interference (CCI) being 1.75·10-5 and 7.35·10-6 respectively. We conclude that wireless communication systems operating at 2.4 GHz microwave frequency can be significantly interfered by lightning.

Lightning Interference in Multiple Antennas Wireless Communication Systems

This paper analyzes the interference of lightning flashes with multiple antennas wireless communication systems operating in the microwave band at 2.4 GHz and 5.2 GHz. A bit error rate (BER) measurement method was used to evaluate BER and packet error rate (PER) during 5 heavy thunderstorms on January 25 and March 17 to 20, 2011, respectively. In addition, BER measurements also were done on January 21 and March 30, 2011 under fair weather (FW) conditions providing a baseline for comparison. The Transmitter-Receiver separation was fixed at 10 meter with line-of- sight (LOS) consideration. We infer that lightning interfered with the transmitted digital pulses which resulted in a higher recorded BER. The maximum recorded BER was 9.9·10 -1 and the average recorded BER and PER were 2.07·10 -2 and 2.44·10 -2 respectively during the thunderstorms with the average fair weather BER and PER values under the influence of adjacent channel interference (ACI) and co-channel interference (CCI) being 1.75·10 -5 and 7.35·10 -6 respectively. We conclude that multiple antennas wireless communication systems operating at the microwave frequency can be significantly interfered by lightning.

Chaotic pulse train in cloud-to-ground and cloud flashes of tropical thunderstorms

In this paper, we report for the first time the observation of chaotic pulse train (CPT) preceding natural subsequent negative return strokes and also CPT occurrence in IC flashes from tropical thunderstorms in South Malaysia. In CG flashes, all CPTs were occurred in between return strokes with 41.1% have occurred between the first and second return strokes. The maximum number of CPT in one sequence is 3, which can be observed between the first and third return strokes only. In IC flashes, all CPTs were observed to occur in between IC flash pulses.

Time-frequency profile of discharge processes prior to the first return stroke

We aim to investigate the time-frequency profile for sets of lightning processes that occurred prior to the first return stroke which include narrow bipolar pulses, preliminary breakdown pulses and stepped leaders. The work is mainly using the wavelet transformation in order to gain the frequency spectrum while not losing the time information of the located pulses. 2 sets of events that include the narrow bipolar pulse (NBP) followed by preliminary breakdown pulses (PBPs), stepped leaders (SLs) and the first return stroke (RS) are used in this paper. All selected data are recorded during northeastern monsoon season at the end of year 2012 in Malaysia. Parameters that used in this works includes the (1) upper and (2) lower frequency spectrum for both spectral and spread regions and (3) power spectrum. In average, the upper and lower frequency spectrum for NBP is at least 10 times higher when compare to the first return stroke. It is also found that the NBP radiates predominantly between 61 kHz and 168 kHz which much higher than the first return stroke with range from 2 kHz to 12 kHz. PBP pulses radiate intensely within 65 kHz to 1 MHz, whereas SL pulses radiate predominantly between 163 kHz and 455 kHz. In terms of power spectrum, PBP pulses tend to produce higher magnitude of power spectrum in the earlier stage and decreased towards the end of its process. In the contrary, SL pulses power spectrum magnitudes are lower in the beginning and tend to increase when approaching to the first return stroke.

Occurrence of narrow bipolar pulses between negative return strokes in tropical thunderstorms

This paper reports a recent observation of Narrow Bipolar Pulses (NBPs) occurrence between return strokes (RSs) of negative cloud-to-ground (CG) flashes in tropical thunderstorms. A wideband electric field antenna measurement system has been used in this work and 173 isolated and non-isolated NBPs managed to be recorded. We found that 22 single NBPs and a pair of positive NBP embedded between RSs and some of them are located within the horizontal distance range from 20 to 45 km from the observation station.

Wavelet analysis of narrow bipolar pulses in tropical region

In this paper, we reported the wavelet analysis of lightning electric field of Narrow Bipolar Pulses (NBP) measured during two different monsoon season in Johor, Malaysia. The lightning electric field of NBP were divided into Narrow positive Bipolar Pulses (NPBP) and Narrow Negative Bipolar Pulses (NNBP). Analysis on the wavelet and frequency spectrum reveals that the energy spectrum for both NBPs concentrates at higher frequency (200 kHz to 600 kHz) in comparison to return strokes. Further, NBPs radiated higher energy power spectrum during northeast monsoon with average peak power spectrum of the initial stage NNBP and NPBP are 76,650 (V/m)2 and 76309 (V/m)2, respectively.

Emission heights of narrow bipolar events in a tropical storm over the Malacca Strait

Emission heights for narrow bipolar events (NBEs) have been reported mostly from observations at mid latitudes but none have been reported from tropical regions. In this paper, we are reporting for the first time the heights of NBE emissions from a tropical storm over the Malacca Strait, a narrow water passage between the Malay Peninsula and Sumatra Island. A total of 49 positive NBEs (+NBEs) were detected from the storm. The NBE activity can be divided into two stages according to the emission heights and radar reflectivity data. The first stage (or S1) lasted for only 6 minutes, started with the first detected NBE, and produced 20 NBEs (41%). The emission heights ranged between 12.0 and 16.7 km. Radar reflectivity data showed that the storm reached maximum values at 55 dBZ within the period S1. In contrast, the second stage (S2) lasted longer (32 minutes) and produced 29 NBEs (59%). The emission heights were lower and ranged from 8.5 to 13.7 km. Radar reflectivity data showed that the storm reached maximum values at 50 dBZ within the period S2.

Wavelet analysis of chaotic pulse trains prior to subsequent return strokes in Malaysia

This paper presents a wavelet transformation of chaotic pulse trains (CPTs) prior to negative subsequent return strokes in Malaysia. A total of 593 recorded waveforms were examined. Even though several hundred waveforms were identified as containing CPTs, only 47 waveforms with CPTs preceding subsequent return stroke were selected for analysis. 19 samples are classified as CPTs associated with dart or dart-stepped leader (Type 1 CPTs) with spectral and spread regions average frequency range of 34.8-154.3 kHz and 56.2-81.4 kHz respectively. 28 samples are classified as chaotic pulse trains alone (Type 2 CPTs) with spectral and spread regions average frequency range of 24.6-121 kHz and 40.3-62 kHz, respectively. The Type 1 CPTs tends to radiate at a higher frequency range compared to Type 2 CPTs. The maximum power radiated by the largest pulse in Type 1 CPTs is more than six times larger than that for the Type 2 CPTs. In addition, the Type 1 CPTs have larger electric field variations, higher frequency, and higher power radiated spectrum compared to Type 2 CPTs. The reported radiated energy can be further compared with other lightning activities to give a better insight on the in-cloud breakdown processes prior to subsequent return strokes.

Wavelet analysis for negative return stroke and narrow bipolar pulses

Lightning generates electric fields are known to have negative consequences. In this study, two types of lightning electric fields which are Negative Return Stroke (NRS) and Narrow Bipolar Pulses were thoroughly analyzed using wavelet analysis. Hence, analysis on the wavelet and frequency spectrum reveal that the energy spectrum for NBP concentrates at high frequency (200 kHz to 500 kHz) with average peak power of the initial stage for NNBP and NPBP are 76,650 (V/m)2 and 76309(V/m)2 respectively. However, the initial stage peak power corresponding to NRS is about 118,931(V/m)2 with lower frequency spectrums (60 kHz). The results suggest that NBP radiates energy at high frequency region compared to NRS. Hence it can be concluded that, electric field pulse for NBP experience more extensive and rapid ionization process compared to NRS.