Applied Mechanics and Materials Vols. 284-287

Abstract: In this paper, a novel cooperative relay scheme based on a symbol constellation expansion is addressed in multipath fading channels. The proposed scheme expands the symbol constellation through a unique combination of the original symbols, thus increasing the minimum distance among the single points. Numerical results demonstrate that the proposed scheme achieves the fourth order cooperative diversity with two relays and has a better bit error rate performance than those of the conventional schemes.

Abstract: In this article the MGF (moment generating function) obtained to determine the ergodic (average) channel capacity, and which is by passing the difficulty in calculating the pdf (probability density function) of SNR (signal-to-noise ratio) traditionally. Some numerical results are offered for validating the accuracy the theoretical deriver formulas. Furthermore, many plots work out from combination with different number of transmitter and receiver for comparison. It is valuable to note that the more the antenna numbers the larger channel capacity is not acceptable when the correlation coefficient is taken into account the system evaluation of a MIMO system.

Abstract: In this paper, we propose a novel carrier frequency offset (CFO) estimation scheme for orthogonal frequency division multiplexing (OFDM) systems. The proposed scheme has much wider estimation range compared with that of the conventional scheme, making it more robust to the fractional FO variation. Numerical results demonstrate that the proposed scheme has better estimation performance than the conventional scheme for wider fractional FO range.

Abstract: This paper presents a wideband wireless receiver front-end for 3.1-5.0GHz band group-1 (BG-1) WiMedia application. The front-end circuits are designed in 0.18um standard CMOS process. The experimental results show the maximum conversion power gain is 45.5dB; minimum noise figure is 2.9dB. Input return loss is lower than -9.3dB and output return loss is lower than -6.8dB. The maximum LO conversion power is 0dBm. 3dB working frequency is 1.9GHz (3.1GHz-5.0GHz) Total power consumption is 24.3mW including LNA, mixer and all buffers. Total chip area is 1.27mm² including dummy and pads.

Abstract: In this paper, we propose a novel maximum likelihood (ML) decoding scheme based on the combination of depth- and breadth-first search methods on a partitioned tree for multiple input multiple output systems. The proposed scheme first partitions the searching tree into several stages, each of which is then searched by a depth- or breadth-first search method, possibly exploiting the advantages of both the depth- and breadth-first search methods in an organized way. Numerical results indicate that, when the depth- and breadth-first search algorithms are adopted appropriately, the proposed scheme exhibits substantially lower computational complexity than conventional ML decoders while maintaining the ML bit error performance.

Abstract: This paper presents a brand new hardware framework of wireless personal area monitoring system (WPAMS) in order to form a point-to-point simply connected personal area identification network with the applications of ubiquitous monitoring personal valuable belongings. The WPAMS consists of sub-1GHz radio frequency identification (RFID) interrogator subsystem, antenna subsystem and passive RFID transponder subsystem with salient features of low-cost, tiny and power-efficient. The hardware frameworks of two commercial interrogator prototypes have been identified and simulated. With the connection of 5.7dBi right-hand circularly polarized antenna and in the adherence of local power regulation (within 1watt), the identified range of all types of commercial transponders from sideward and upward directions can be reached to 2 meters. The current PCB size of interrogator is 88mm45mm and can be reduced in the near future.

Abstract: MANETs become a considerable interest nowadays. However, these types of networks are vulnerable to a large group of attacks, e.g., MAC layer attacks. Most of the previous researches related to security issues focus on detection of misbehaviors after it occurred. We propose a new way of thinking to evade occurrence of misbehaviors. A novel clustering algorithm is presented using analytic hierarchy process to elect clusterhead. Afterwards, the clusterhead is required to assign backoff values to originators in its transmission range, which are also the members in the corresponding cluster, rather than permitting the originators to choose backoff values. Meanwhile, the elected clusterhead also monitors whether originators obey the backoff values. With the proposed scheme, the misuse of the backoff in MAC layer in 802.11 DCF can be prevented.

Abstract: This study analyzes and calculates unipolar and bipolar coded configurations of spectral-amplitude-coding optical division multiple access (SAC-OCDMA) systems by using analytic and simulated methods. The important feature of the SAC-OCDMA systems is that multiple access interference (MAI) can be eliminated by code sequences of a fixed in-phase cross-correlation value. This property can be effectively canceled by multiple access interference by using balance detection schemes. This study uses Walsh-Hadamard codes as signature codes for the unipolar and bipolar schemes. The coder and decoder structures are based on optical filters of fiber Bragg gratings (FBGs). The simulation results of unipolar/bipolar coding structures are first presented by commercial simulation obtained using OptiSystem software. The simulation results show that the bit error rate (BER) through use of the bipolar coding method is superior to the unipolar scheme, especially when the received effect power is large. The eye diagram also shows that the bipolar encoding structure exhibits a wider opening than the unipolar encoding structure.

Abstract: In this study, we propose optical code-division multiple-access (OCDMA) network for the radio-over-fiber (RoF) transmissions. The network encoder/decoders (codecs) are structured on the basis of arrayed-waveguide-grating (AWG) routers coded with modified prime codes (MPCs). Performances are numerically evaluated with the effect of phase-induced-intensity-noise (PIIN). It showed that the new code families with lower cross correlation can suppress the intensity noise and cancel out the multiple-access interference (MAI) in balanced detection process effectively and hence improve the system performance. By the proposed MPC-coded OCDMA ROF network codecs, each network requires only two AWG routers to accomplish spectral coding of radio base station (RBS) and decoding of control station (CS), thus, resulting in a simpler and lower cost system. It is possible to accomplish interference- and crosstalk-free optical CDMA system for RoF transmissions.

Abstract: Very high frequency (VHF) is widely used in radio and television broadcasting. In order to improve the quality of service (QoS) and signal transmission distance, the repeaters be applied to lengthen the transmitting distance of VHF and expand the coverage of radio stations. Under ensuring the QoS, the reduction cost is very important. In this paper, focusing on the different coverage of repeaters, we discuss the minimum number of repeaters to cover a whole circular area, and the square model and cellular model are proposed. Then we analyze the case in view of the simplex communication and duplex communication. Furthermore, the influence of the location of the radio station to the minimum number of repeaters needed is discussed. Finally, we discuss how the minimum number of repeaters changes with the change of the numbers of radio stations. The minimum number of repeaters to cover the circle area will increase as the radius of the repeaters coverage decreases. The radio station in the center of the circle flat can broadcast to the farthest area and the radio station in the fringe area can’t broadcast to farther area. In simplex communication, the minimum number of repeaters with n radio stations in the circle are is n-1 times greater than that with only one radio station.