Performance simulation of NC-PRMA with signatures in microcellular communication systems

Packet reservation multiple access (PRMA) improves capacity in microcellular systems compared with time division multiple access (TDMA) or frequency division multiple access (FDMA). In PRMA, when a mobile terminal has information packets to transmit, it contends with other terminals for access to a common radio channel. Therefore the main performance degradation is due to the collision of terminals simultaneously transmitting packets. In this paper we propose a non-collision PRMA (NC-PRMA) protocol with signatures to achieve a better performance than PRMA does. Two classes of duplexing schemes, frequency division duplexing (FDD) and shared time division duplexing (STDD), are explored and two speech activity models, slow and fast, in both FDD and STDD schemes are studied. From the results of a computer simulation it is observed that, with the constraint of a packet-dropping rate no greater than 0·01, NC-PRMA can support 38 (43) and 45 (49) users respectively under the FDD and STDD schemes if the slow (fast) speech activity detector is adopted. © 1998 John Wiley & Sons, Ltd.     

Resource Management Techniques for OFDM Systems with the Presence of Inter-Carrier Interference

The aim of the paper is to study the problems of resource management in the presence of inter-carrier interference (ICI) and multipath fading channel for orthogonal frequency division multiplexing (OFDM) systems. OFDM is a promising technique for the broadband wireless communication systems. However, the OFDM communication system is sensitive to ICI which arises because of Doppler spread and carrier frequency offset (CFO). To solve these problems, an optimization method has been exploited, and a computationally efficient method using numerical optimization techniques is proposed. The simulation results show that these derived optimal solutions and proposed suboptimal algorithms as compared with the uniform power allocation algorithm or conventional water-filling algorithm can significantly improve the performance of the OFDM systems.     

Steroid and cembranoids from the Dongsha atoll soft coral Lobophytum sarcophytoides

A novel sterol, sarcophytosterol (1), and four new cembranoids, sarcophytolins A-D (2-5), have been isolated from the soft coral Lobophytum sarcophytoides along with four known metabolites 6-9. The relative structures of new metabolites were elucidated on the basis of extensive spectroscopic analyses and X-ray diffraction analysis of 1, and the absolute configurations of 1 and 5 were determined by Mosher’s method and CD spectrum, respectively. Compound 1 is a steroid possessing an unusual (20R,23R,24R)-23,24-dimethyl-20-hydroxy side chain. Compounds 3, 6, 8, and 9 were shown to exhibit cytotoxicity toward a limited panel of cancer cell lines. Furthermore, while 1 could effectively enhance the expression of the pro-inflammatory iNOS protein in LPS-stimulated RAW264.7 macrophage cells, compounds 2, 3, 5-7 and 9 were found to effectively inhibit the accumulation of the pro-inflammatory of iNOS.     

A Novel Convergence Accelerator for the LMS Adaptive Filter

Due to its ease of implementation, the least mean square (LMS) algorithm is one of the most well-known algorithms for mobile communication systems. However, the main limitation of this approach is its relatively slow convergence rate. This paper proposes a booster using the Markov chain concept to speed up the convergence rate of LMS algorithms. The nature of Markov chains makes it possible to exploit past information in the updating process. According to the central limit theorem, the transition matrix has a smaller variance than that of the weight itself. As a result, the weight transition matrix converges faster than the weight itself. Therefore, the proposed Markov-chain based booster is able to track variations in signal characteristics and simultaneously accelerate the rate of convergence for LMS algorithms. Simulation results show that the Markov-chain based booster allows an LMS algorithm to effectively increase the convergence rate and further approach the Wiener solution. This approach also markedly reduces the mean square error while improving the convergence rate.     

Low-Complexity Butterfly Integration Structure for MMSE-SIC SISO Detector

In this paper, we propose a low-complexity butterfly integration structure (LCBIS) for the minimum mean square error-soft interference cancellation (MMSE-SIC) soft-in soft-out (SISO) detector, which is widely used for MIMO systems. Unlike the conventional MMSE-SIC SISO detector which performs matrix inverse operations, the LCBIS performs butterfly integration operations with low complexity. To develop the LCBIS SISO detector, we derive an integral expression for the extrinsic information of the conventional MMSE-SIC SISO detector, and then propose a butterfly integration structure to compute the integral expression efficiently. Without matrix inverse operations, LCBIS significantly reduces the complexity of the MMSE-SIC SISO detector. In addition, simulation results show that LCBIS can offer much better BER than the other SISO detectors which do not perform matrix inverse operations.     

Secolridoids Glycosides from Jasminum amplexicaule

In addition to jaslanceosides B ( 1 ) and E ( 2 ), and jasminoside ( 3 ), a new secoiridoid glucoside, isojasminoside ( 4 ) was isolated from the leaves of Jasminum amplexicaule (Oleaceace). The structure of 4 was determined on the basis of spectral analysis and chemical reactions. Chemotaxonomy for some selected plants in Jasminum is also discussed.     

Distributed Power Balancing with Linear Prediction and Adaptive On-Off Strategies for CDMA Cellular Mobile Systems

Several distributed balance (DB) power control algorithms that can achieve SIRbalance have already been proposed for cellular mobile systems [1–3].In the present paper, two simple strategies, namely linear prediction andadaptive on-off strategies, are further applied to forward link distributedbalance (DB) power control in DS/CDMA cellular mobile systems. The linearprediction is used to track the variance of the short-term fading andcompensate it in advance, and the adaptive on-off strategy is applied to solvethe problem that the received SIR of all the communication links less than theminimum required SIR. Simulation results indicate that DB power control withthese two strategies can achieve much better performance than the original DBpower control.     

The effect of multipath interference on the performance of packetradios

The effect of multipath interference on the performance of packet radios is investigated. The protocols considered include pure ALOHA and slotted ALOHA. Signal reception with and without capture effect is considered in the analysis. Mathematical expressions of system throughput and packet delay have been successfully obtained for each protocol. Numerical calculations are used to demonstrate when the multipath interference can be ignored and when it can be disastrous     

3Alpha,7alpha,12alpha-triacetoxy-5beta-cholanic acid, a steroid from the Formosan soft coral Alcyonium sp. (Alcyoniidae)

Chemical investigation of the organic extract of a soft coral belonging to the genus Alcyonium furnished a steroid, 3alpha,7alpha,12alpha-triacetoxy-5beta-cholanic acid (1). The structure of steroid 1 was assigned on the basis of spectroscopic evidence, particularly in 1D and 2D NMR experiments. The configuration of steroid 1 was further supported by molecular mechanics calculations.     

Briaexcavatins C-F, four new briarane-related diterpenoids from the Formosan octocoral Briareum excavatum (Briareidae)

Four new briarane-related diterpenoids, designated as briaexcavatins C-F (1-4), were isolated from the Formosan octocoral Briareum excavatum, collected off southern Taiwan coast. The structures of these new metabolites were elucidated by the interpretation of spectroscopic and chemical methods. The configuration of 1 was further supported by molecular mechanics calculations. Briarane 1 has been shown to exhibit mild cytotoxicity toward MDA-MB-231 human breast tumor cells and briarane 3 was found to show activity to inhibit neutrophil elastase release in humans.