Applied Mechanics and Materials Vols. 284-287

Abstract: Quality of service (QoS) is so significant that it cannot be neglected in the recent evolution of wireless mobile networks, which are characterized by great heterogeneity. Handoff delay is one of the problematic issues that users are facing in the heterogeneous networks. In the wireless networks, many mobile users still cannot obtain the network resources they need when applying real-time services while handoff occurs. Consequently, providing a seamless handoff for QoS connections in heterogeneous wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX) is crucial. In this paper, a resource ReSerVation Protocol (RSVP) extension scheme for seamless handoff in heterogeneous WLAN/WiMAX networks is proposed. The proposed scheme is based on QoS aware mobility architecture to guarantee a certain degree of QoS. The network selection is initiated by the mobility of the mobile station (MS) and pre-handoff is performed, basing on received signal strength (RSS). Simulation results show that the proposed scheme outperforms the previous schemes.

Abstract: There are two scenarios that proactive fast HCoP-B (FHCoP-B) cannot normally complete its operations due to fast movements during handover. We will propose efficient reactive FHCoP-B flows for these two scenarios to support fast and seamless handovers. We will further extend the analytical model proposed for mobile IPv6 to investigate performance metrics of reactive FHCoP-B with the radio link protocol, which can detect packet losses and performs retransmissions over the error-prone wireless link. Through simulations, FHCoP-B outperforms HCoP-B and the other two NEMO schemes by achieving shortest handover latencies only with few extra buffer spaces.

Abstract: The performance improvement on SIP-based VoIP server is given in this paper. The signaling server “SIP Proxy Server” and media streaming server “Media Relay Server” are applied. Firstly, the performance of VoIP server is analyzed and evaluated in detail. Then the effective method is applied to improve the performance of VoIP server. In the analysis results of SIP Proxy Server, the CPU time for the registration and call-setup sessions need 3.241 ms and 7.985 ms respectively. Moreover, in the Media Relay Server system, when the packet size from 1 to 32 bytes, the maximum throughput of packet is about 82,000 and 16,000 per second for UDP and TCP respectively. The large the packet, the less throughput is tenable. There are three methods applied to improve the performance. The capacity by 31 times is achieved. The capacity with 3,524 calls for each Media Relay Server is achieved. The improved method proposed in this paper is reasonable.

Abstract: IEEE 802.11 based wireless networks are extensively used in mesh, ad hoc, and sensor networks due to less expense and easier deployment. IEEE 802.11a/b/g standard supports multi-rate and multi-channel settings to facilitate network transmissions. Many researchers focus on maximizing network throughput and propose channel assignment algorithms in IEEE based multi-rate multi-channel (M²) wireless networks. Less works are devoted to the study of network capacity in M² wireless networks. In our observation, static channel assignment algorithms for maximizing network throughput may limit network capacity, and the improvement on network capacity comes mainly from higher data rate communication links. Therefore, we model the optimization problem and derive the optimization formula in detail. Subsequently, we propose an efficient channel assignment algorithm, Partial Bit Strings Pruning (PBSP) channel assignment to maximize network capacity. The results of associated simulations show that the performance of our PBSP channel assignment algorithm is superior to the algorithm based on the well-know minimum-interference approach.

Abstract: Packet loss is one of the most essential problems in speech communication. It will cause the information loss and uncomfortable for listeners in voice over IP. This investment proposed an approach based on waveform similarity measure using overlap-and-Add algorithm. The waveform similarity overlap-and-add (WSOLA) technique is an effective algorithm to deal with packet loss concealment (PLC). For real-time time communication, the WSOLA algorithm is widely used to deal with the length adaptation and packet loss concealment of speech signal. Time scale modification of audio signal is one of the most essential research topics in data communication, especially in voice of IP (VoIP). Herein, we proposed the dual-side WSOLA that is derived by standard WSOLA. Instead of only exploitation one direction speech data, the proposed method will reconstruct the lost voice data according to the preceding and cascading voice. The dual-side WSOLA can use both the past and future speech signal waveform to reconstruction voice waveform of lost packet. The evaluations show that the quality of the reconstructed speech signal of the dual-side WSOLA is higher than that of the standard WSOLA and GWSOLA on different packet loss rate and length using the metrics: PESQ and MOS. The significant improvement is obtained by dual side information in the proposed method. The proposed dual-side waveform similarity overlap-and-add (DSWSOLA) outperforms the traditional approaches.

Abstract: In this paper we demonstrate a new technology in which we use the spatial optical modulation with trigger pulse width and pulse width modulation of light source (LED,LD) to build the near-infrared electro-optics modulation coding system (NIEOMCS). Using the optical coupler to let the pulse modulation near infrared LED collimated light of transmitter enter into an optical fiber and spatial optical modulator, the electro-optics modulation signal is then detected by the photodiode of the receiver. Because of aperture module with three changeable stop sizes and three duty cycles of light signal, there are 27 kinds of code modes in this system. When the receiver aperture is smaller than the correlation length of fading and the observation interval is shorter than the correlation time of fading, the modulation code error rate of the modulation system occurring is less than 0.2%.

Abstract: A novel design of photonic crystal waveguide crossing based on multimode-interference (MMI) structure is proposed. Two structures of difference device lengths are simulated and studied. The proposed structures have high transmission efficiency for a wide bandwidth. The crosstalk is -26dB with device length of 12 lattice periods and -39dB with device length of 24 lattice periods. The plane wave expansion method and finite-difference time-domain method are used to calculate the modal dispersion curve and field propagation, respectively. The proposed MMI-based waveguide crossing has the potential to be practical in high-density optical integrated circuits.

Abstract: The Light Emitting Diode (LED) is a highly efficiency light source, normally controlled by pulse width modulation (PWM) with intelligent environment condition sensing. While the connection between the control center and LED devices could be wireless or cable-connected, the power lines always have cables, and the signaling cable could be bundled with the power cables. Given a large number of fixed devices and a medium distance between devices, DMX512 physical signaling could serve as an appropriate good protocol for the control system. This paper proposes a method to implement a multi-color (RGB) LED programmable control system on chip for increased flexibility and scalability. The implementation comprises a command set architecture customized for RGB-color LEDs, composed of setup, action and query commands, and includes a special visible method to indicate device ID.

Abstract: We present the microsphere coupled Mach–Zehnder interference structure. We theoretically calculate that spectral responses of this structure vary with the glucose solution concentrations. It can produce the sharply asymmetric Fano resonance line shape related to the slope between zero and unity transmission. The variation of the normalized transmission is linearly related to the solution concentration. This structure is the promising highly sensitive biochemical sensor due to high quality factor resonance and steep slope over a very narrow frequency range

Abstract: In this work, we used a fiber splicer to fabricate a long-period grating (LPG) in a photonic crystal fiber (PCF) for power loss measurement. Photonic crystal fiber grating (PCFG) is long-period grating which is produced by using electric arc to heat the PCF. For the measurement of power loss, we will use beam profile and power meter to analyze in detail the phenomenon of loss factor and parameter of the measurement. We will also do experiment on both polished and unpolished long-period photonic crystal fiber grating and compare the results. Utilizing two long-period grating of photonic crystal fiber (polished and unpolished) to analyze and compare the difference of optical field distribution and power loss. The unpolished PCFG shows the equally filed distribution with wavelength by beam profile measurement. But, the polished PCFG is sensitive with wavelength that the field distribution of wavelengths 1520 and 1530nm are concentrated on the upper half of field distribution and the wavelength 1530nm is more concentrated on the side. The wavelength of polished long-period grating of photonic crystal fiber has sensitive response and loss with wavelength increase and increment. Another measurement is probing photonic crystal fiber grating of power loss measurement using power meter. The PCFG can be evaluated by field distribution and power for operating wavelength and power loss. The measurement of operating wavelength of the long-period fiber grating is 1550nm.