Mohamad Yusoff Alias

Cyclic prefix reduction for 20.48 Gb/s direct-detection optical OFDM transmission over 2560 km of SSMF

Optical Orthogonal Frequency Division Multiplexing (O-OFDM) provides major advantages in mitigating Group-Velocity Dispersion (GVD) in Single Mode Fiber (SMF). Unfortunately, when the uncompensated long-haul transmission ranges become very large, substantial dispersion is accumulated. Owing to the large accumulated dispersion, the Cyclic Prefix (CP) duration will occupy a substantial fraction of the OFDM frame. This effect sets some limitations on the overall throughput and the spectral efficiency. Moreover, the transmission is inefficient because of the energy wastage contained within the CP. In the case where the CP length is shorter than the Channel Impulse Response (CIR), energy wastage is reduced but the system performance is limited by the Inter Symbol Interference (ISI) and Inter Carrier Interference (ICI). To overcome this problem, a Time Domain Equalizer (TEQ) immediately after the channel is proposed. It can cancel the residual ISI and ICI caused by both the GVD and the CP length being shorter than the CIR. The simulation results show that, using BER of 10−3 as a reference, the system performance improves by 2.69thinspacedB while considering 6-feedforward/5-feedback-weight Decision Feedback TEQ (DF-TEQ) and 2.03 dB while considering 10-tap Least Mean Square TEQ (LMS-TEQ) even though the CP length is shorter than the CIR. This method reduces size of the CP, and consequently the performance of the system will be improved. Copyright

End-to end delay performance analysis of various codecs on VoIP Quality of Service

Voice over Internet Protocol (VoIP) services are susceptible to Internet Protocol (IP) network burstiness causing packets drop and momentary gap in the call. The main objective of this paper is to study the effect of various voice codec schemes on the VoIP Quality of Service (QoS). Popular voice codecs such as G.711, G.729A Conjugate-Structure Algebraic-Code-Excited Linear-Prediction (CS-ACELP), G.723.1 and G.726 Adaptive Differential Pulse Code Modulation (ADPCM) are studied and VoIP simulation models are built. The voice codec performance is determined with the best performance codec identified. From the simulations, the end-to-end delay (Ta) results for each of the users were obtained. The results were averaged out to gain the average end-to end delay (Ta) for every simulation. From the simulation results it can be seen that for most of the locations, G.711 without using silence suppression has the highest average end-to-end delay (Ta). On the other hand, G.723.1 with silence suppression has the lowest average Ta.

Cognitive VANET with enhanced priority scheme

Vehicular communications are important to ensure emergency messages are transmitted on time to prevent accidents. Therefore, in recent years, various standardization bodies and automobile companies have developed vehicular ad hoc network (VANET) to ensure public road safety. The current IEEE802.11p schemes utilize only traffic type to categorize priority levels. However, accidents are prone to occur when vehicles are in close distance. Therefore, based on the latest standard draft of IEEE1609.4 and IEEE802.11p, the proposed scheme, namely Enhanced Priority VANET Scheme (EPVS) is proposed where distance range between vehicles is derived and transmission priority level is categorized based on reliable distance range and data type. Performance of the proposed EPVS is evaluated in Vehicles in Network Simulation (Veins) with road traffic simulator, Simulation of Urban mobility (SUMO) using a realistic urban map. Simulations results show that the proposed EPVS results in lower average delay, in comparison with the default IEEE802.11p scheme.

On performance analysis of LS and MMSE for channel estimation in VLC systems

Channel estimation is a key feature for wireless optical communication systems. This paper presents an evaluation of channel estimation techniques for indoor visible light communication (VLC) systems using a direct current-biased optical orthogonal frequency division multiplexing (DCO-OFDM) scheme. The VLC system can simultaneously provide illumination and wireless communication at a high data rate. However, the coverage area is limited and the distance is about 3 m. In this paper, performance analysis of two channel estimation methods is presented, one using the least squares (LS) algorithm and the other the minimum mean square error (MMSE) algorithm, to estimate channel response by applying them to various M-QAM modulations. The performance of these two methods is compared by mathematical analysis and by simulation by measuring bit error rate (BER) and mean square error (MSE) versus signal-to-noise ratio (SNR). The results shown that, at higher SNR, the MMSE algorithm outperforms the LS for both BER and MSE.

Design and implementation of adaptive scalable streaming system over heterogeneous network

Distribution of multimedia content through the internet has gain popularity with the advancement of multimedia technology through software application with different transmission capabilities. Current conventional system implementation works perfectly for a guaranteed network bandwidth. However, when the packet experience losses due to drop in bandwidth, it could not preserve an acceptable video quality over the heterogeneous network. Thus, if the bandwidth could be determined in real-time, an application that controls the scalability of video stream sent over the channel can be used to control the video quality. This is done by reducing the bit-rate of the video to be sent according to current available bandwidth. In this paper, a scalable video streaming system with automate bandwidth control over heterogeneous network, using spatial scalability approach and end-to-end available bandwidth estimation are designed and implemented. Distribution of multimedia data streaming would be improved without any jitter and could fit to any devices with various performance capabilities.

Subband decomposition techniques for adaptive channel equalisation

In this contribution, the convergence behaviour of the adaptive linear equaliser based on subband decomposition technique is investigated. Two different subband-based linear equalisers are employed, with the aim of improving the equalisers convergence performance. Simulation results over three channel models having different spectral characteristic are presented. Computer simulations indicate that subband-based equalisers outperform the conventional fullband linear equaliser when channel exhibit severe spectral dynamic. Convergence rate of subband equalisers are governed by the slowest subband, whereby different convergence behaviour in each individual subband is observed. Finally, the complexity of fullband and subband equalisers is discussed.

Joint optimization and threshold structure dynamic programming with enhanced priority scheme for adaptive VANET MAC

Nodes in vehicular ad-hoc network (VANET) are highly mobile, traversing in unpredictable and varying environment. Therefore, contention window size and transmission power should adapt according to the high mobility transmission environment. In this paper, we propose an adaptive VANET medium access control (MAC) layer with joint optimization for VANET (MACVS) which aims at minimizing average delay and maximizing packet success rate. An adaptive joint optimization with proposed threshold structure dynamic programming, with closed loop feedback control system, is designed to optimize contention window size and transmission power. Adaptive optimization is done based on road traffic conditions and transmission reliable distance range (depicted by interference and noise), by monitoring the continuous change and threshold of received signal strength to interference and noise ratio. Mathematical expressions have been developed for the MACVS optimization framework, and the produced analytical results show good agreement with the simulation results. Simulations with different arrival rates and urban map of city center show that the proposed MACVS with low complexity joint optimization effectively reduces end-to-end delay while achieving high packet success rate under various network traffic condition.

Performance analysis of DCO-OFDM in VLC system

The performance of indoor visible light communication (VLC) systems using a direct current-biased optical orthogonal frequency division multiplexing (DCO-OFDM) scheme is investigated in this paper. The impact of nonlinearity of Light Emitting Diode (LED) and its beam angle on the VLC system performance is studied. We later analyze the effect of modulation order, number of subcarriers, signal scaling and biasing operation on the peak to average power ratio (PAPR) which is a major issue in OFDM based VLC system. Simulation results show that the bit error rate (BER) decreases as the degree of nonlinearity increases and a better BER can be achieved as the LED behavior approaches linear model. In addition, it is shown that reducing the QAM order or increasing the number of subcarriers may reduce the effect of the LED nonlinearity, thus improving the BER performance of the VLC system. Moreover, it is demonstrated that PAPR is higher for a large number of subcarriers and modulation order. Finally, the PAPR of the visible light OFDM system can significantly be reduced by employing the signal scaling combined with biasing operation.

Improving VANET Performance with Heuristic and Adaptive Fuzzy Logic Scheme

Abstract Rapid topology change in vehicular ad hoc network (VANET) is common due to the inherent high mobility nodes and unpredictable environments in VANET. In order to ensure efficient packet transmission, nodes in VANET should react adaptively to topology change in VANET. In this paper, we present a new heuristic and adaptive fuzzy logic scheme (HaFL), which adapts the contention window size and transmission power according to network and traffic conditions. The current existing schemes in VANET utilize only a single parameter to optimize the contention window and transmission power without consideration on the effects of interference as one of the main factors in VANET transmission degradation. In VANET, packet loss can occur at different stages of transmission due to interference or due to elapsed time. In the proposed HaFL, fuzzy logic is used to adaptively optimize the contention window size based on three parameters namely collision rate, SINR and queue overflow which represent packet drop at different stages of transmission. Transmission power which is usually a static parameter is also optimized with consideration on the effects of VANET interference in the proposed HaFL. The performance of the proposed HaFL is evaluated in Vehicles in Network Simulation with road traffic simulator, Simulation of Urban mobility. Simulation results show that the proposed HaFL demonstrates adaptability with improved throughput, low end-to-end delay and higher packet success rate in comparison with the default IEEE802.11p and existing schemes.

User data rate enhancement using heterogeneous LTE-802.11n offloading in urban area

Data offloading is a method to significantly improve network capacity. Offloading of data from macro-cells to pico-cells helps to ease capacity demand in hotspot areas where user distribution is dense and often demanding high bandwidths per user. This study uses a heterogeneous network using combined Long Term Evolution - WiFi IEEE 802.11n coverage to improve the capacity performance of the network. The heterogeneous network uses the offloading mechanism to enhance the per user capacity of the heterogeneous network. The user distribution is non-uniform and the 802.11n Access Points are positioned in areas with high user density. The offloading mechanism is based on a WiFi-First algorithm where users with sufficient Received Signal Strength to hop on to WiFi will be offloaded while the rest of the users will remain on the LTE network. A real digital map of Kuala Lumpur in the geospatial vector data format,. TAB is used for the simulations. The simulation results show that although around 50% of the users are offloaded to WiFi, the LTE network is only relieved 2.75% of the total capacity usage. This may seem small but due to offloading, nearly 100% increase in average capacity in experienced by the remaining LTE users from 0.05 Mbps to 0.09967 Mbps. The offloaded users also experience an increase of 0.876Mbps on average per user.