Aimed at the research actuality of displacement distribution measurement of each point at the measured object surface in condition of micro-motion, we developed a high-speed image sensor based on low-speed CCD in this paper, which can be used for vibration measurement. The operating principle of the sensor and the collecting principle of synchronization data are analyzed. The sensor combined with sinusoidal phase-modulating (SPM) interferometry was used in vibration distribution measurement. Thus each vibration displacement of the measured object surface was gotten. So the displacement distribution measurement of a low cost, high-speed and high precision was realized.
The resonant frequency measurement of cantilever has an important position in MEMS(Micro Electro Mechanical Systems) research. Meanwhile the SPM interferometry is a high-precision optical measurement technique, which can be used in physical quantity measurement of vibration, displacement, surface profile. Hence, in this paper we propose to apply SPM(SPM) interferometry in measuring the vibration of MEMS cantilever and in the experiment the vibration of MEMS cantilever was driven by light source. Then this kind of vibration was measured in nm precision. Finally the relational characteristics of MEMS cantilever vibration under optical excitation can be gotten and the measurement principle is analyzed. This method eliminates the influence on the measuring precision caused by external interference and light intensity change through feedback control loop. Experiment results prove that this measurement method has a good effect.
This paper presents a new approach for quality of service (QoS) support in optical burst switching (OBS) networks. In the approach, the data channels of an outgoing link at a core node are divided into multiple groups, with each group corresponding to a service class. The number of data channels in each group is mainly determined by data traffic. In general, a data burst (DB) can be sent on a data channel reserved by its burst head packet (BHP) only in its own group. Upon failing to reserve any bandwidth in its own group, the BHP tries to re-reserve even preempt bandwidth on a data channel in a lower-priority group. A lower-priority BHP can't reserve bandwidth on any data channel in a higherpriority group. In addition, this paper also investigates the reasonable relation between the preempting DB length and the preempted DB length.
The stream control transmission protocol (SCTP) will play an important role in the next generation of the Internet. Up to now, there are no literatures about differentiated services for SCTP associations. Regarding the throughput as SCTP criteria to support differentiated services, the differentiated services between SCTP associations can be obtained by introducing the weighted factor to a or b for AIMD(a,b)-based SCTP congestion control. Theoretic analysis and simulation results show that the proposed scheme can achieve well proportional differentiated services for SCTP associations with few additional overheads, and it is easy to regulate the fluctuation of data sending rate or SCTP response to networks.
To mitigate TCP global synchronization and improve network throughput, an improved TCP congestion control mechanism is proposed, namely P-TCP, which adopts the probability-based way to adjust congestion window independently when the network occurs congestion. Therefore, some P-TCP connections may decrease the congestion window greatly while other P-TCP connections may decrease the congestion window lightly. Simulation results show that TCP global synchronization can be effectively mitigated, which leads to efficient utilization of network resources as well as the effective mitigation for network congestion. Simulation results also give some valuable references for determining the related parameters in P-TCP.
TCP congestion control mechanism, being based on the presupposition that network congestion is the only reason for data loss, is suitable for wired environments rather than for wireless environments with characteristics of higher bit error rate, lower bandwidth, longer delay, frequent mobility and so on, where link corruption can also cause data loss. To avoid unnecessary decrease of packet sending rate resulting in lower throughput and longer delay, some improved TCP congestion mechanisms have been presented. However, one of the disadvantages of these mechanisms is that a great deal of unnecessary packets lost by corruption can be caused while heavy data loss rate by corruption lasts short time. As well known, energy consumption of mobile hosts is one of the most important factors for wireless communication. How to save energy of mobile host has become an important task for wireless communication. One of the methods is to improve reliability to decrease overheads resulting from re-transmitting lost data. Obviously, it is necessary to decrease data sending rate, but how does it do? This paper answers the question, and then presents an improved TCP congestion control mechanism, namely TCP_IR (TCP for Improving Reliability) whose implementations are based on two algorithms. Algorithm I-based TCP_IR is driven by data sending periodic, while algorithm II-based TCP_IR is driven by the event of data lost by corruption. They can be very easily implemented with fewer overheads and can effectively improve TCP reliability with light influence to throughput and delay. The paper’s contribution is to give valuable references to further study TCP in wireless networks.
Recently, there is an increasing interests in providing differentiated services in Internet. However, research efforts have almost exclusively focused on routers by improving their policies of packet scheduling and queue management. There has been much less work on transport level approaches to support differentiated services. The mechanism presented by Chang-Biao Xu, DSAS-TCP and MulTCP are the only pieces of the works in this direction known to the authors. Up to now, there is no paper to discuss the interrelation between these mechanisms. Regarding throughput as TCP criteria to support proportional-differentiated-services (PDS), this paper deeply explores the variants of AIMD(a,b)-based TCP congestion control and their effect on differentiated services, and presents a transport level approach for TCP to support PDS, namely PDS_TCP which can be obtained by introducing weighted factor to a or b of AIMD(a,b)-based TCP congestion control. PDS_TCP also takes into account the influence of slow start for timeout. From the analysis, this paper draws the conclusion that the existing mechanisms are only variants of PDS_TCP. For the example of PDS_TCP, the principles, implementation and simulation results of PDS_a_TCP are discussed in detail. The theory analysis and simulation results show that the proposed mechanism PDS_TCP can be implemented with lower additional overheads and support controlled PDS very well without the loss of flexibility.