Kaharudin Dimyati

S-band multiwavelength Brillouin/Raman distributed Bragg reflector fiber lasers.

A multiwavelength Brillouin/Raman distributed Bragg reflector fiber laser operating in the S-band region is proposed and demonstrated. The laser uses a 7.7 km long dispersion-shifted fiber with an effective mode area of 15 μm(2) as the Brillouin and Raman gain media simultaneously. Two 1420 nm laser diodes with a combined power of 372 mW are used as pump sources, while a fiber Bragg grating with a center wavelength of 1500 nm is used as a reflector in the cavity. The setup is capable of generating 6 clearly defined Stokes lines at the highest pump power, spanning from 1499.8 to 1500.3 nm with the even Stokes having relatively higher peak powers, between 1.4 and 3.5 dBm as compared to the odd Stokes, which have peak powers between -4.7 and -5.0 dBm. The output of the laser is very stable and shows little to no fluctuations over a monitoring period of 50 min.

A New SIR-Based Sigmoid Power Control Game in Cognitive Radio Networks

Interference resulting from Cognitive Radios (CRs) is the most important aspect of cognitive radio networks that leads to degradation in Quality of Service (QoS) in both primary and CR systems. Power control is one of the efficient techniques that can be used to reduce interference and satisfy the Signal-to-Interference Ratio (SIR) constraint among CRs. This paper proposes a new distributed power control algorithm based on game theory approach in cognitive radio networks. The proposal focuses on the channel status of cognitive radio users to improve system performance. A new cost function for SIR-based power control via a sigmoid weighting factor is introduced. The existence of Nash Equilibrium and convergence of the algorithm are also proved. The advantage of the proposed algorithm is the possibility to utilize and implement it in a distributed manner. Simulation results show considerable savings on Nash Equilibrium power compared to relevant algorithms while reduction in achieved SIR is insignificant.

A novel utility function for energy-efficient power control game in cognitive radio networks.

Spectrum scarcity is a major challenge in wireless communications systems requiring efficient usage and utilization. Cognitive radio network (CRN) is found as a promising technique to solve this problem of spectrum scarcity. It allows licensed and unlicensed users to share the same licensed spectrum band. Interference resulting from cognitive radios (CRs) has undesirable effects on quality of service (QoS) of both licensed and unlicensed systems where it causes degradation in received signal-to-noise ratio (SIR) of users. Power control is one of the most important techniques that can be used to mitigate interference and guarantee QoS in both systems. In this paper, we develop a new approach of a distributed power control for CRN based on utility and pricing. QoS of CR user is presented as a utility function via pricing and a distributed power control as a non-cooperative game in which users maximize their net utility (utility-price). We define the price as a real function of transmit power to increase pricing charge of the farthest CR users. We prove that the power control game proposed in this study has Nash Equilibrium as well as it is unique. The obtained results show that the proposed power control algorithm based on a new utility function has a significant reduction in transmit power consumption and high improvement in speed of convergence.

Radiated Emission from Handheld Devices with Touch-Screen LCDs

Handheld communication devices fitted with touch-screen LCDs do emit some kind of electromagnetic radiation (EMR) even though they were not designed to do so. There is potential for the emission can be intercepted and reconstructed for eavesdropping or even intelligence purposes. Information leakage from hand-held devices can be valuable information for the intelligence communities. This paper presented discussions on how much unintentional emission is radiated from these devices. Comparison on the level of emission is made based on manufacturers and sizes of LCD.

Deployment of a 3D tag tracking method utilising RFID

Recent trend shows that one of the crucial problems faced while using radio frequency to track the objects is the inconsistency of the signal strength reception, which can be mainly due to the environmental factors and the blockage, which always have the most impact on the tracking accuracy. Besides, three dimensions are more relevant to a warehouse scanning. Therefore, this study proposes a highly accurate and new three-dimensional (3D) radio frequency identification-based indoor tracking system with the consideration of different attenuation factors and obstacles. The obtained results show that the proposed system yields high-quality performance with an average error as low as 0.27 m (without obstacles and attenuation effects). The obtained results also show that the proposed tracking technique can achieve relatively lower errors (0.4 and 0.36 m, respectively) even in the presence of the highest attenuation effect, e = 3.3 or when the environment is largely affected by 50% of the obstacles. Furthermore, the superiority of the proposed 3D tracking system has been proved by comparing with other existing approaches. The 3D tracking system proposed in this study can be applicable to a warehouse scanning.

Intelligent Ray-Tracing: an efficient indoor ray propagation model

This study proposes an efficient and accelerated Intelligent Ray-Tracing (IRT) algorithm based on Binary Angle Division (BAD) technique for radio signal prediction in indoor area. The intelligent features of the proposed IRT can skip the processing of the unnecessary signals based on the invalid region and reduce the number of candidate objects (obstacles) as well as their edges while performing ray-object intersection tests, which can make the algorithm faster as well as more accurate. The obtained results are compared with the existing indoor ray propagation methods to prove the superiority of the proposed IRT technique in terms of both computational efficiency and accuracy of signal prediction.

Recent efficient iterative algorithms on cognitive radio cooperative spectrum sensing to improve reliability and performance

In cognitive radio (CR), cooperative spectrum sensing (CSS) has been extensively explored to be accounted for in a spectrum scanning method that permits secondary users (SUs) or cognitive radio users to utilize discovered spectrum holes caused by the absence of primary users (PUs). This paper focuses on optimality of analytical study on the common soft decision fusion (SDF) CSS based on different iterative algorithms which confirm low total probability of error and high probability of detection in detail. In fact, all steps of genetic algorithm (GA), particle swarm optimization (PSO), and imperialistic competitive algorithm (ICA) will be well mentioned in detail and investigated on cognitive radio cooperative spectrum sensing (CRCSS) method. Then, the performance of CRCSS employing GA-, PSO-, and ICA-based scheme is analysed in MATLAB simulation to show superiority of these schemes over other conventional schemes in terms of detection and error performance with very less complexity. In addition, the ICA-based scheme also reveals noticeable convergence and time running performance in comparison to other techniques.

On the robustness of measurement of reliability stopping criterion in turbo iterative decoding

Measurement of reliability (MOR) stopping criterion is able to terminate early in the low and high signal-to-noise ratio (SNR) while maintaining the bit error rate (BER) performance. However, the performance of MOR is only based on one code structure and hence, the robustness of MOR is still unknown in turbo iterative decoding. Thus, this paper will test the robustness of MOR based on the following parameters: frame size, code structure, channel reliability and code rate. Then, we analyse and compare the average iteration number (AIN) and the BER performance of MOR with the benchmark stopping criterion known as Genie to determine the robustness of MOR. From the analysis, MOR has a BER degradation for low code rate. MOR also fails to perform well if the corret channel reliability is not available at the receiver and this results a large degradation in BER performance. However, MOR has close performance to Genie in terms of BER for various frame sizes, code structures and high code rate with the assistance of correct channel reliability. MOR is also able to save AIN at low SNR as compared to Genie and this can reduce delay and complexity of turbo codes.

Early stopping turbo iteration at low SNR for CE-based stopping criteria

The Cross-Entropy-based (CE-based) stopping criteria advantage is able to terminate early in the high signal-to-noise ratio (SNR) while maintain the bit error rate (BER) performance. Unfortunately, the criteria fails to cope with low SNR region and make the decoder iterates until maximum or infinite iteration. This paper proposed an early termination technique at low SNR for the CE-based stopping criteria using the decoding threshold derived by the measurement of reliability (MOR) at low SNR. In the simulation results and analysis, we compare the average iteration number (AIN) and the bit-error rate (BER) performance between the proposed combination methods with the existing CE-based stopping criteria. From the results, the combination method capable to reduce the AIN at low SNR with minimum one AIN while maintaining the AIN at high SNR as the traditional method. This significant reduction could reduce delay and complexity of existing CE-based stopping criteria while maintaining the BER performances.