Improvement of delay spread immunity by using symbol timing synchronisation based on maximum likelihood estimation for 16 QAM/TDMA diversity receivers

Symbol timing synchronisation (STSYNC) based on maximum likelihood estimation and a receiver configuration in which each branch independently estimates optimum STSYNC timing are proposed to improve delay spread immunity for I6 QAM/TDMA diversity receivers. Computer simulation confirms that the proposed STSYNC and receiver configuration can improve delay spread immunity by approximately 30%.<>     

A spectrally efficient constant envelope modulation technique forPCS and mobile communications

A newly developed constant envelope FQPSK modem/radio architecture, which employs a modified double-jump (DJ) filter in the cross-correlated FQPSK system, is proposed for personal communications systems (PCS) and mobile radio applications. Power efficiency, spectrum efficiency, BER, and system capacity of this system are investigated in a non-linear amplified (NLA) Rayleigh fading environment. We demonstrate that with the simplest threshold detectors (binary robust eye diagrams in I and Q channels), this system is 4-7 dB more power efficient than the US digital cellular and Japanese Handyphone standard π/4-QPSK, 50%-100% more spectrally efficient than the European standard GMSK, and it almost double the capacity of GMSK     

Modems for emerging digital cellular-mobile radio system

Digital modem techniques for emerging digital cellular telecommunications-mobile radio system applications are described and analyzed. In particular, theoretical performance, experimental results, principles of operation. and various architectures of π/4-QPSK (π/4-shifted coherent or differential QPSK) modems for second-generation US digital cellular radio system applications are presented. The spectral/power efficiency and performance of the π/4-QPSK modems (emerging American and Japanese digital cellular standards) are studied and briefly compared to GMSK (Gaussian minimum-shift keying) modems (proposed for European DECT and GSM cellular standards). Improved filtering strategies and digital pilot-aided (digital channel sounding) techniques are also considered for π/4-QPSK and other digital modems. More spectrally efficient modem trends for future cellular mobile (land mobile) and satellite communication system applications are also highlighted     

An improved channel coding algorithm for low-frequency spectralsuppression

An improved low-frequency spectral suppression (LOFS) code is introduced and analyzed as a method to suppress low-frequency energy in a digital baseband signal with significantly lower redundancy than required methods. Alternatively, the LOFS code will suppress more energy near DC with a given redundancy when compared to current coding methods, allowing insertion of a pilot tone which leads to a simple unambiguous carrier recovery subsystem that can track system-induced noise. The LOFS code reduces redundancy by adding control bits in word format for multilevel signals, that is, control bits for multiple frames are inserted in one symbol duration. Use of this LOFS code could reduce the redundancy of currently used digital transmission systems from 4% to 1%. Analysis of computer simulations shows that a premodulation high-pass filter, while significantly degrading the uncoded PAM signal, causes little degradation of the coded data and keeps data to pilot interference to a minimum. Experimental hardware results are included to verify simulation results     

Structure and properties of polyimide‐bonded magnets processed from prepolymers based on diacetyl derivatives of aromatic diamines and dianhydrides

We report a novel method of polyimide (PI) synthesis from prepolymers based on dianhydrides and diacetyl derivatives of aromatic diamines that facilitate the preparation of a melt processable mixture at 300 ± 10°C of the prepolymer and magnetic Nd‐Fe‐B alloy to provide PI‐bonded magnets with enhanced properties. It is shown that chemical structure of the prepolymers strongly influences viscosity behavior via crystallization of the oligoimide in the melt, leading to formation of PI with rigid‐rod like structure. This structural ordering of the prepolymers based on diacetyl derivative of diamine used in this study, if not controlled, leads to exponential increase of melt viscosity with time, making it practically impossible to prepare melt processable mixture of the magnetic particles and the PI prepolymers at elevated temperatures. The results obtained demonstrate that appropriate dianhydrides and diacetyl derivatives of diamines that do not lead to crystallization of oligoimides in prepolymer mixture can be used under controlled processing conditions to prepare melt‐processable PI‐bonded magnets containing rigid‐rod like PI structure that significantly increases thermal stability of the magnets. The temperature dependencies of the magnetic properties of the PI‐bonded magnets under conditions that they are likely to encounter during their service life were found to be remarkably similar to that of commercial thermoplastic magnets such as injection‐molded nylon magnets. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 478–485, 2006     

Viscosity reduction of isotonic solutions of the photosensitizer TPCS2a by cyclodextrin complexation

Meso-tetraphenyl chlorin disulphonate (TPCS_2a) is a photosensitizer (PS) particularly developed and patented for use in the technology of photochemical internalization (PCI) against cancer. TPCS_2a is known to aggregate in aqueous media even at low concentrations (≥0.1?µM) and to form a high-viscosity network at clinically relevant concentrations (mM). The aim of this work was to evaluate the effect of two hydroxypropylated cyclodextrin derivatives of beta and gamma type, respectively i.e. HPβCD and HPγCD, on the aggregation and solubilization of TPCS_2a in isotonic solutions. Samples containing micromolar concentrations of TPCS_2a were studied spectrophotometrically, while samples containing a clinical relevant concentration (10?mM?=?9?mg/ml) of TPCS_2a were evaluated by dynamic viscosity measurements. HPβCD was determined to be a more suitable solubilizer of TPCS_2a than HPγCD in aqueous media both in the absence and presence of salt. The complexation stoichiometry between TPCS_2a/HPβCD at micromolar to millimolar concentrations of TPCS_2a was determined to be 1:3 and 1:2 in the absence and presence of isotonic NaCl, respectively. The network of TPCS_2a (10?mM) was broken down in the presence of 3% w/v (=?20?mM) HPβCD, i.e. a 1:2 molar ratio between TPCS_2a and the cyclodextrin. Formation of the inclusion complex resulted in low viscosity samples both in water and in the presence of isotonic NaCl or phosphate buffered saline (PBS) at 25?°C and 37?°C.     

A new FQPSK modem/radio architecture for PCS and mobile satellitecommunications

A newly developed constant envelope FQPSK modem/radio architecture, which employs a modified double-jump (DJ) filter in the cross-correlated FQPSK system, is proposed for personal communications systems (PCS) and mobile satellite applications. The power efficiency and spectrum efficiency of this system are investigated in a nonlinear amplified (NLA) environment. The bit error rate (BER) performance is evaluated in a noisy Rayleigh fading channel. We demonstrate that with the simplest threshold detectors (binary robust eye diagrams in I and Q channels), this system is 4-7 dB more power efficient than the US digital cellular and Japanese Handyphone standard π/4-QPSK (50%-100% more spectrally efficient than the recently adopted wireless local area network (LAN) standard GFSK and the European standard GMSK). The results indicate that the proposed DJ filtered FQPSK is a power and spectrally efficient modem/radio technique. By selecting different system parameters, this system can be optimized for a wide range of applications in PCS and mobile satellite communications     

Nonobvious correlation properties of quadrature GMSK, a modulationtechnique adopted worldwide

GMSK is the world's most widely used modulation technique for mobile digital telephony and digital wireless applications. We describe two GMSK modulator structures, the voltage controlled oscillator (VCO) and the quadrature modulator structure. The tremendous advantages of the quadrature modulator structure for practical GMSK modulator implementations are emphasized. We present the results of computer simulations and hardware experimental measurements performed on GSM-standardized IC chips which are used by several million subscribers in order to illustrate the operation of a GMSK modulator. Since quadrature modulator structures are used in nearly all practical GMSK chipsets, the properties of this structure are of wide interest. In this paper we highlight the crosscorrelation properties of the GMSK in-phase and quadrature-phase baseband signals, which are part of the quadrature modulator structure. While uncorrelated in-phase and quadrature-phase baseband signals are used in traditional QPSK and OQPSK modulated systems, we demonstrate that there is strong crosscorrelation between the in-phase and quadrature-phase baseband signals. The crosscorrelation is stronger if the observation interval is shorter. Nonobvious quadrature modulator/radio crosscorrelation advantages were patented by Kato/Feher (1986). Design with crosscorrelated quadrature transmitter is “contrary to the wisdom of classical linear communications theory”. Crosscorrelated quadrature modulated systems include FQPSK-KF and GMSK     

Phenols as defensive secretion in a Malayan cockroach,Archiblatta hoeveni vollenhoven

A sternal abdominal defensive gland in adults of the Malayan cockroachArchiblatta hoeveni is described. It producesp-cresol and as a minor compound, phenol. When the animals are attacked, they eject the secretion as a spray that can be aimed in the direction of, the stimulus. The position, morphology, and chemistry of the gland support the taxonomic position ofArchiblatta within the Blattoidea.