Showing papers by "Borhanuddin Mohd Ali published in 2014"

An Efficient Backoff Algorithm for IEEE 802.15.4 Wireless Sensor Networks

Abstract: IEEE 802.15.4 is one of the most prominent MAC protocol standard designed to achieve low-power, low-cost, and low-rate wireless personal area networks. The contention access period of IEEE 802.15.4 employs carrier sense multiple access with collision avoidance (CSMA/CA) algorithm. A long random backoff time causes longer average delay, while a small one gives a high collision rate. In this paper, we propose an efficient backoff algorithm, called EBA-15.4MAC that enhances the performance of slotted CSMA/CA algorithm. EBA-15.4MAC is designed based on two new techniques; firstly, it updates the contention window size based on the probability of collision parameter. Secondly, EBA-15.4MAC resolves the problem of access collision via the deployment of a novel Temporary Backoff (TB) and Next Temporary Backoff (NTB). In this case, the nodes not choose backoff exponent randomly as mentioned in the standard but they select TB and NTB values which can be 10–50 % of the actual backoff delay selected by the node randomly. By using these two new methods, EBA-15.4MAC minimizes the level of collision since the probability of two nodes selecting the same backoff period will be low. To evaluate the performance of EBA-15.4MAC mechanism, the network simulator has been conducted. Simulation results demonstrate that the proposed scheme significantly improves the throughput, delivery ratio, power consumption and average delay.

A low computational complexity V-BLAST/STBC detection mechanism in MIMO system

Abstract: The idea of multiple antenna arrays has evolved into multiple-input multiple-output (MIMO) system, which provides transmit and receive diversities. It increases robustness of the effect of multipath fading in wireless channels, besides yielding higher capacity, spectral efficiency and better bit error rate (BER) performance. The spatial diversity gain is obtained by transmitting or receiving multiple copies of a signal through different antennas to combat fading and improves the system BER performance. However, the computational complexity of MIMO system is inevitably increased. Space-time coding (STC) technique such as Alamouti's space-time block code (STBC) that combines coding, modulation and signal processing has been used to achieve spatial diversity. Vertical Bell Laboratories Layered Space-Time (V-BLAST) uses antenna arrays at both the transmitter and receiver to achieve spatial multiplexing gain. Independent data streams that share both frequency bands and time slots are transmitted from multiple antennas and jointly detected at the receiver. The theoretical capacity of V-BLAST increases linearly with the number of antennas in rich scattering environments. It's well-known that maximization of spatial diversity gain leads to degradation of spatial multiplexing gain or vice versa. In order to achieve spatial multiplexing and diversity gains simultaneously, the V-BLAST/STBC scheme has been introduced. This hybrid scheme increases MIMO system capacity and maintains reliable BER performance at the same time. However, both V-BLAST and STBC layers, in this hybid scheme, assume each other as an interferer. Thus, the symbols must be decoded with a suitable detection mechanism. In this paper, a new low complexity detection mechanism for V-BLAST/STBC scheme based on QR decomposition, denoted as low complexity QR (LC-QR) decomposition, is presented. The performance of the proposed LC-QR decomposition detection mechanism in V-BLAST/STBC transceiver scheme is compared with other detection mechanisms such as ZF, MMSE and QR decomposition. It is shown that the BER performance in V-BLAST/STBC scheme is better than V-BLAST scheme while its system capacity is higher than orthogonal STBC scheme when the LC-QR decomposition detection mechanism is exploited. Moreover, the computational complexity of proposed LC-QR decomposition mechanism is significantly lower than other abovementioned detection mechanisms.

Power Efficiency in Broadband Wireless Communications

Abstract: Power Efficiency in Broadband Wireless Communications focuses on the improvement of power efficiency in wireless communication systems, especially of mobile devices. Reviewing cutting-edge techniques for conserving power and boosting power efficiency, the book examines various technologies and their impact on consumer devices. It considers each technology, first by introducing the main physical layer components in recent wireless communication systems along with their shortcomings, and then proposing solutions for overcoming these shortcomings.The book covers orthogonal frequency division multiplexing (OFDM) signal generation and formulation and examines the advantages and disadvantages of OFDM systems compared to alternative multiplexing. It introduces one of the main drawbacks of OFDM systems, peak-to-average power ratio (PAPR), and discusses several PAPR techniques. It also explains how to overcome the main drawbacks of real-world OFDM system applications. Considers power amplifier linearization for increasing power efficiency and reducing system costs and power dissipation Describes the implementation scenario of the most promising linearization technique, digital predistortion Presents some experimental demonstrations of digital predistortion when the device under test is in the loop Because the most costly device in a communication system that has a direct impact on power efficiency and power consumption is the power amplifier, the book details the behavior and characteristics of different classes of power amplifiers. Describing the evolution of the mobile cellular communication system, it details a cost-effective technique to help you increase power efficiency, reduce system costs, and prolong battery life in next generation mobile devices.

Intercomparison of Methods for Determination of Resonant Frequency Shift of a Microstrip Patch Antenna Loaded with Hevea Rubber Latex

Abstract: This paper presents an intercomparison between the finite element method, method of moment, and the variational method to determine the effect of moisture content on the resonant frequency shift of a microstrip patch loaded with wet material. The samples selected for this study were Hevea rubber latex with different percentages of moisture content from 35% to 85%. The results were compared with the measurement data in the frequency range between 1 GHz and 4 GHz. It was found that the finite element method is the most accurate among all the three computational techniques with 0.1 mean error when compared to the measured resonant frequency shift. A calibration equation was obtained to predict moisture content from the measured frequency shift with an accuracy of 2%.

Reduction of Outage Probability Due to Handover by Mitigating Inter-cell Interference in Long-Term Evolution Networks

Abstract: will increase the signalling exchanges between the serving eNB and the target eNB, resulting in increased ICI. This is overcome by means of our proposed Soft Frequency Reuse (SFR). Simulation results using LTE-Sim show that the outage probability and delay are reduced by 24.4% and 11.9% respectively, over the HHO method, which is quite significant.

Energy-aware cluster based cooperative spectrum sensing for cognitive radio sensor networks

Abstract: Energy efficient spectrum sensing and data communication to extend the lifetime of cognitive radio sensor network is becoming increasingly important due to resource constraint of CR-WSN inherent from WSN. This paper presents an energy-aware clustering (EAC) algorithm that enhances spectrum sensing performance and reduces network energy consumption thereby prolonging lifetime of the network. We derived network wide energy consumption model in terms of spectrum sensing energy consumption, intra cluster and inter clusters energy consumptions, and then determined the optimal number of clusters for the network. Through numerical analysis, we evaluate the effectiveness of the proposed algorithm in terms of minimizing network wide energy consumption and improving spectrum sensing performance.

Multicast-Unicast Data Delivery Method in Wireless IPv6 Networks

Abstract: Multicast IPv6 is an efficient way of transmitting data simultaneously to a group of IPv6 users. It has the advantage of reducing the required bandwidth of IPv6 data delivery compared to unicast transmission. The data rate of multicast transmission over WLAN is confined by the user with the lowest rate in the multicast group, which is called the fixed base rate problem. This paper proposes a delivery method that incorporates both multicast and unicast transmissions to solve the fixed base rate problem. The proposed method divides the IPv6 network into two levels: multicast mode for the upper level of the network [IPv6 server to Access Point (AP)], and unicast mode for the lower level (AP to mobile nodes). To maintain the end-to-end multicast transmission, the AP is responsible for converting multicast packets to unicast packets. Such a combination enables the proposed method to inherit the advantages of both multicast and unicast transmissions. The performance of our proposed method is evaluated in a test-bed environment that considers the transmission of real-time video application. The proposed multicast-unicast is able to improve the throughput and video quality experienced by the end user, with low packet loss and transmission delay.

Power amplifier linearisation scheme to mitigate superfluous radiations and suppress adjacent channel interference

Abstract: Power amplifiers are one of the costly devices in wireless communication systems and exhibit non-linearity. The problem of non-linearity in the power amplifier categorises in two disturbance impacts, output distortion and in-band distortion which lead to adjacent channel interference and constellation deviation, respectively. In order to gain maximum efficiency of the power amplifier and reduce interference, the authors propose a new digital pre-distortion scheme called complex gain convergence (CGC). The proposed scheme is compared with indirect learning architecture and validated against an laterally diffused metal oxide semiconductor (LDMOS) power amplifier. The outcome of applying CGC scheme shows enhancement in adjacent channel leakage ratio and error vector magnitude performance while the complexity is even lower. An experimental demonstration with the actual power amplifier is also presented.

A crest factor reduction scheme based on recursive optimum frequency domain matrix

Abstract: One of the main imperfections in orthogonal frequency division multiplexing (OFDM) techniques is a peak-to-average power ratio (PAPR) or crest factor (CF). High crest factor signal forces a power amplifier in communication systems to back-off which leads to power efficiency degradation. Several techniques have been proposed in literature to mitigate the high peaks in OFDM signal; however most of them suffer from complexity and PAPR performance. In conventional SLM (C-SLM), increasing the number of inverse fast Fourier transform (IFFT) leads to excessive hardware resources requirement and increases system cost. In this paper a novel crest factor scheme based on recursive optimum frequency domain matrix is proposed which requires only two IFFT which results in significant reduction in the computational complexity. Simulation results show both the complexity and crest factor are reduced significantly compared to the conventional methods.

A NEMO-HWSN solution to support 6LoWPAN network mobility in hospital wireless sensor network

Abstract: IPv6 Low-power Personal Area Networks (6LoWPANs) have recently found renewed interest because of the emergence of Internet of Things (IoT). Mobility support in 6LoWPANs for large-scale IP-based sensor technology in future IoT is still in its infancy. The hospital wireless network is one important 6LoWPAN application of the IoT, it keeps continuous monitoring of vital signs of moveing patients. Proper mobility management is needed to maintain connectivity between patient nodes and the hospital network. In this paper, first we survey IPv6 mobility protocols and propose a solution for a hospital architecture based on 6LoWPAN technology. Moreover, we discuss an important metric like signaling overload to optimize the power consumption and how it can be optimized through the mobility management. This metric is more effective on the mobile router as a coordinator in network mobility since a mobile router normally constitutes a bottleneck in such a system. Finally, we present our initial results on a reduction of the mobility signaling cost and the tunneling traffic on the mobile PAN.

Peak-to-average power ratio reduction based on Cross-Correlation in OFDM systems

Abstract: Two of the most important techniques of Peak-to-average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) systems are Partial Transmit Sequence PAPR (PTS-PAPR) and Cross-Correlation-PTS. This paper investigates a complete analysis on these two techniques providing simulation and discussion of their performance on PAPR reduction and bit error rate (BER). Moreover the comparison of these methods by using Saleh model amplifier in an OFDM system is provided. The results show that PTS-PAPR outperforms the Cross-Correlation-PTS in terms of PAPR performance while Cross-Correlation-PTS method is more efficient in BER reduction.

Scalable and efficient key management for Mobile WiMAX networks

Abstract: SUMMARY Efficiency and security are two critical but often conflicting issues in Multicast and Broadcast Service of IEEE 802.16e technology. Hence, it is vital to ensure an optimal scenario where neither security concerns, nor operational efficiency of the network is compromised. This paper proposes a new key management scheme called Scalable and Efficient Key Management Protocol, which uses a binary tree structure together with a B-tree of order 2 structure. It focuses on improving key management performance of the existing techniques in terms of efficiency and scalability, without a loss in security. Scalable and Efficient Key Management Protocol dynamically establishes subgroups based on the current number of Mobile Stations in a WiMAX Base Station's coverage area. This will optimize the communications, computational and storage costs of the network. In addition, the scheme guarantees strong network scalability. Both analytical and simulation approaches have been carried out, and the results showed that the proposed scheme exhibits superior performance in terms of efficiency and scalability compared with existing schemes. Copyright © 2012 John Wiley & Sons, Ltd.

Compensation of frequency independent I/Q imperfections using LMS algorithm

Abstract: Due to the increasing demand of high data rate in recent years, orthogonal frequency division multiplexing (OFDM) and Direct up conversion transmitters (DCT) have gained significant interest. However such system's efficiency can be compromised by front-end impairments such as In-phase Quadrature (I/Q) imperfections. In this paper the effects of IQ imbalance on transmitter is studied and an adaptive algorithm is developed to compensate such distortions. Simulation results show high level of accuracy in the proposed algorithm and its ability to estimate the IQ imperfections. It also shows that the proposed compensator could overcome the imperfections perfectly.

A recursive optimum frequency domain matrix to reduce crest factor in OFDM systems

Abstract: One of the main imperfections in orthogonal frequency division multiplexing (OFDM) technique is a peak-to-average power ratio (PAPR) or crest factor (CF) High crest factor signal forces a power amplifier in communication systems to back-off which leads to power efficiency degradation Several techniques have been proposed in literature to mitigate the high peaks in OFDM signal; however most of them suffer from complexity and PAPR performance In this paper a novel crest factor scheme based on recursive optimum frequency domain matrix is proposed which requires only two IFFT which results in significant reduction in the computational complexity Simulation results show both the complexity and crest factor are reduced significantly compared to the conventional methods

High reliability of real-time visual data transmission using superposition coding with receiver diversity

Abstract: Supporting visual data applications in the real-time communication systems are among the most challenging issues over the next generation wireless communication systems This challenge is further magnified by the fact that the quality of reception is highly sensitive to transmission delay, data losses and bit error rate (BER) in such applications In this paper, we proposed Superposition Coding with Receiver Diversity (SPC-RD) scheme, which employs unequal error protection (UEP) to improve the error performance, maximize the received signal to noise ratio (SNR) and optimize the reliability of the transmission system In the transmitter side, the visual data is divided into a number of different priority layers based on their effects on the reception quality These layers are modulated individually where the highest priority layer is modulated with the highest UEP level against error-prone channels, and vice versa These modulated signals are then superimposed together and transmitted via wireless Single-Input Multiple-Output (SIMO) Rayleigh fading channel In the receiver side, three different diversity combining approaches; selection combining (SC), equal gain combining (EGC) and maximal ratio combining (MRC) are considered The combined signal is then passed through a multiuser demodulator so-called the ordered successive interference cancellation (O-SIC) demodulator to reconstruct and separate the data layers This demodulation technique is evaluated and compared with the traditionally maximum likelihood joint detection (MLJD) technique Extensive simulations have been carried out to validate the various assertions Under the assumption of equal transmission power, the simulation results illustrate that the proposed SPC-RD scheme provides a SNR gain of 145 dB over the Rayleigh fading channel at the diversity order of three for the acceptable BER level of 10?3 when BPSK scheme is exploited compared to the traditional equal error protection system In addition, the proposed scheme with O-SIC demodulation technique achieves almost similar performance compared to MLJD technique but using less computational complexity

A peak to average power ratio reduction scheme to increase power efficiency in broadband communication systems

Abstract: Enhanced partial transmit sequence (EPTS) and cross-correlation-PTS are two techniques for reducing peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. EPTS is a low complexity technique compared to conventional partial transmit sequence (CPTS) and cross-correlation-PTS techniques which outperforms the cross-correlation-PTS in terms of PAPR reduction while cross-correlation-PTS technique is more efficient in BER reduction. This proposed technique is a novel serial combination of the above-mentioned techniques to provide both sufficient PAPR reduction and BER reduction simultaneously. Simulation results are carried out with QPSK modulation and Saleh model power amplifier. From the simulation results the proposed technique achieves about 0.5 and 1.5 dB PAPR reduction compared to EPTS and cross-correlation-PTS techniques, respectively, when it outperforms EPTS in terms of BER performance.

Enhanced Marking Process (EMP) for Constructing Dominating Set in Mobile ad-hoc Networks with Unidirectional Links

Abstract: Broadcasting or flooding is one of the principal functions in wireless ad-hoc networks In broadcasting, a mobile node sends the same message to all nodes in the network in one-to-all model Broadcasting based on set of dominating nodes is remunerative approach, where the broadcasting activity is constrained to only the nodes in the dominating set A set is dominating if all nodes in the network are either in the set or neighbors of nodes in the set In this study, the notion of constructing connected-dominating-set is extended to ad-hoc networks with unidirectional links An enhanced distributed algorithm is presented that is based on the marking process which is has been introduced in earlier work Our enhanced algorithm features a good locality properties since it need only 2-hop neighborhood information within each node The algorithm checks for the mutual existence of nodes in the neighbor table of their neighbors to guarantee the symmetric connectivity between neighboring nodes The proposed algorithm is integrated with AODV routing protocol to generate a connected dominating set that will be responsible on flooding activity The efficiency of our approach is investigated and verified through simulation whereas the computational complexity is determined and compared with that of original marking process All the simulations run are carried out with QualNet Simulator version 502

Two-dimensional burst construction with QoS assurance for OFDMA mobile WiMAX system

Abstract: IEEE 80216 OFDMA systems have gained much attention for their ability to support high transmission rates and broadband services For multiuser environments, IEEE 80216 OFDMA systems require a resource allocation algorithm to use the limited downlink resource efficiently One of the main problems to increase the resource utilization and throughput is how to construct two-dimensional blocks that realize time and frequency dimensions to multi-users However, mapping a rectangular shape (ie two-dimensional burst) that not enough to utilize some flows in downlink frame, decreases total throughput and is crucial for Quality of Service (QoS) that support real-time applications In this paper, we propose a low complexity algorithm called Best Edge Block Oriented (BEBO) which complies with 80216 downlink burst characteristics with assurance of real time throughput The proposed algorithm reduce the unserved slots by assembling bursts in the edge of the free spaces for reducing outdoor spaces from other bursts; and enlarge the internal burst size gradually to minimize the internal free spaces for a given request size with priority level and channel state information considerations Simulation results show that the burst construction mechanism result is competitive