DYNAMIC RESOURCE ALLOCATION SCHEME UNDER TRAFFIC CONDITION IN SATELLITE SYSTEMS

As the traffic distribution in China mainland is far from uniform, a new traffic model in China mainland is presented on the basis of per-capita Gross Domestic Product (GDP) and density of population. Based on this characteristic traffic model, a new Traffic Dependent Dynamic Channel Allocation and Reservation (TDDCAR) technique is proposed, the simulation model is built, and the strategies’ performance is evaluated through computer simulation. The simulation results show that, compared to the conventional Fixed Channel Allocation (FCA), TDDCAR estimates the traffic con-ditions in every spot beam and frequently adjusts the traffic according to current traffic conditions. It has achieved a significant improvement in new call blocking probability, handover blocking probability, and fair index, particularly, in heavy traffic conditions. The building of traffic model in China mainland and the analysis of the simulation results has been a key foundation for the study of resource allocation schemes in the future.     

Mitigating adjacent channel interference in vehicular communication systems

In the last few decades, dedicated wireless channels were specifically allocated to enable the development and implementation of vehicular communication systems. The two main protocol stacks, the WAVE standards proposed by the IEEE in the United States and the ETSI ITS-G5 in Europe, reserved 10 MHz wide channels in the 5.9 GHz spectrum band. Despite the exclusive use of these frequencies for vehicular communication purposes, there are still cross channel interference problems that have been widely reported in the literature. In order to mitigate these issues, this paper presents the design of a two-stage FIR low-pass filter, targeting the integration with a digital baseband receiver chain of a custom vehicular communications platform. The filter was tested, evaluated and optimized, with the simulation results proving the effectiveness of the proposed method and the low delay introduced in the overall operation of the receiver chain.     

Effects of carrier phase estimation on front-end IQ mismatch compensation in mode division multiplexed MIMO coherent receiver

The effects of carrier phase estimation on IQ mismatch compensation are investigated and compared for coherent MIMO optical receiver. We investigate the impacts of phase IQ mismatch on required optical signal-to-noise ratio (OSNR) for coherent MIMO detection. The impacts of number of modes and analog-to-digital converter (ADC) resolution are also evaluated. The results show that decision-directed carrier phase estimator could compensate significant amount of IQ mismatch without employing additional compensation technique, and relaxes requirement of ADC resolution.     

Channel length influenced contribution of hole and electron trapping effect to threshold voltage stability in organic field effect transistors

Effect of channel length on hysteresis and threshold voltage shift in copper phthalocyanine (CuPc) based organic field effect transistors was studied. Contrary to expectation, longer channel length devices exhibited minimum threshold voltage shift. Influence of channel length on the contribution of hole and electron trapping to threshold voltage stability was determined. Shortest channel length devices exhibited highest electron trapping effect while longest channel devices exhibited minimum hole as well as electron trapping. Lower hole trap effect for longer channel length devices was suggested to be due to reduced longitudinal field between source and drain electrodes while minimum electron trapping was attributed to suppression of drain current by increased hole trap centres.     

Time reversal acoustic communication receivers: DSP implementation and fast channel estimation

A communication system is implemented on digital signal processors (DSPs) for the underwater acoustic environment. The implemented receiver uses time reversal multi-channel combining followed by a single-channel decision feedback equalizer. Periodic channel estimation is employed to track the channel fluctuations. These techniques are used to mitigate time-varying inter-symbol interference, which is the main challenge in the underwater acoustic channel at operating frequencies greater than 10 kHz. Various optimization tasks are performed to reduce the receiver computational complexity. A fast implementation of the matching pursuit algorithm is tested on the DSP platform. Its performance, in terms of accuracy and run-time, is compared with that of the basic matching pursuit algorithm. Experimental results of the transmission and demodulation of binary phase-shift keying signals at three different symbol rates were obtained in the local Delaware Bay. The low bit error rates demonstrate the effectiveness of our implementation.     

The first principles investigation of ferrite magnetic response with mismatch stress

The quasi-ferrite model is proposed and an appropriate PBE exchange functional with the spin density functional theory(SDFT) is selected for the calculation of the relation between magnetic moment and residual stress in ferrite using a quantum mechanics code. The relationship between ferrite magnetism and the carbon content is determined,and then a ferrite interstitial solid solution(ISS) model in a low carbon concentration state is replaced with an α- Fe model in the case of majority magnetic calculation. The band structure of the loaded-Fe is compared with that of the unloaded α-Fe. The comparison shows that the energy of Fe atomic 3d orbital changes a little,while the energy of electron orbital of iron core below 3d almost keeps unchanged. The relationship between the magnetic moment and the stress appears intermittent due to the Bragg total reflection. The change in the magnetic moment due to lattice mismatch is much larger than that caused by mechanical loading.     

面向VANETs的服务质量的一种信道分配的新算法

车辆的高速移动,导致频繁地进行呼叫切换,这就使得信道分配成为车联网VANETs( Vehicular Ad Hoc Network)中最受关注的研究热点。为此,提出一种新的信道分配算法,标记为SBC算法。该算法引用信道再使用技术( Channel Reuse Technique)、信道借用( Channel Borrowing),并依据车辆行驶的速度计算发生切换的时间,从而提高服务质量QoS( Quality of Service)。仿真结果表明,提出的SBC算法在呼叫阻塞概率、丢失率和切换时延方面表现良好的性能。     

Tubular structures bearing channels in organic crystals composed of adamantane-based macrocycles

Five macrocyclic molecules (1–5) were efficiently synthesized from the dimerization and trimerization of di-substituted adamantane derivatives, which were composed of three different aromatic units and two different linker groups. Three single-crystals were obtained from these macrocyclic molecules, including a set of pseudopolymorphs (3a and 3b) of macrocycle 3 and another macrocycle 5 (5a). Single crystal X-ray analysis revealed that the three monocyclic compounds were rectangular or square in shape with solvent molecules in the cavity. Macrocycle 3 in 3a formed stacks to produce tubular structures with channels that assembled into three-dimensional networks through CH/π interactions.     

Efficient cross polarization with simultaneous adiabatic frequency sweep on the source and target channels

In this work, we propose a new and efficient heteronuclear cross polarization scheme, in which adiabatic frequency sweeps from far off-resonance toward on-resonance are applied simultaneously on both the source and target spins. This technique, which we call as Simultaneous ADIabatic Spin-locking Cross Polarization (SADIS CP), is capable of efficiently locking both the source and target spins with moderate power even in the presence of large spectral distribution and fast relaxation. It is shown that by keeping the time-dependent Hartmann-Hahn mismatch minimal throughout the mixing period, polarization transfer can be accelerated. Experiments are demonstrated in a powder sample of L-alanine.