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北京联合大学毕业设计（论文）任务书题目：OFDM调制解调技术的设计与仿真实现专业：通信工程指导教师：张雪芬学院：信息学院学号：2011080331132班级：1101B姓名：徐嘉明一、外文原文Evolution Towards 5G Multi-tier Cellular WirelessNetworks:An Interference ManagementPerspectiveEkram Hossain, Mehdi Rasti, Hina Tabassum, and Amr AbdelnasserAbstract—The evolving fifth generation (5G) cellular wireless networks are envisioned to overcome the fundamental challenges of existing cellular networks, e.g., higher data rates, excellent end-to-end performance and user-coverage in hot-spots and crowded areas with lower latency, energy consumption and cost per information transfer. To address these challenges, 5G systems will adopt a multi-tier architecture consisting of macrocells, different types of licensed small cells, relays, and device-to-device (D2D) networks to serve users with different quality-of-service (QoS) requirements in a spectrum and energy-efficient manner. Starting with the visions and requirements of 5G multi-tier networks, this article outlines the challenges of interference management (e.g., power control, cell association) in these networks with shared spectrum access (i.e., when the different network tiers share the same licensed spectrum). It is argued that the existing interference management schemes will not be able to address the interference management problem in prioritized 5G multitier networks where users in different tiers have different priorities for channel access. In this context, a survey and qualitative comparison of the existing cell association and power control schemes is provided to demonstrate their limitations for interference management in 5G networks. Open challenges are highlighted and guidelines are provided to modify the existing schemes in order to overcome these limitations and make them suitable for the emerging 5G systems.Index Terms—5G cellular wireless, multi-tier networks, interference management, cell association, power control.I. INTRODUCTIONTo satisfy the ever-increasing demand for mobile broadband communications, the IMT-Advanced (IMT-A) standards have been ratified by the International Telecommunications Union (ITU) in November 2010 and the fourth generation (4G) wireless communication systems are currently being deployed worldwide. The standardization for LTE Rel-12, also known as LTE-B, is also ongoing and expected to be finalized in 2014. Nonetheless, existing wireless systems will not be able to deal with the thousand-fold increase in total mobile broadband data [1] contributed by new applications and services such as pervasive 3D multimedia, HDTV, VoIP, gaming, e-Health, and Car2x communication. In this context, the fifth generation (5G) wireless communication technologies are expected to attain 1000 times higher mobile data volume per unit area,10-100 times higher number of connecting devices and user data rate, 10 times longer battery life and 5 times reduced latency [2]. While for 4G networks the single-user average data rate is expected to be 1 Gbps, it is postulated that cell data rate of theorder of 10 Gbps will be a key attribute of 5G networks.5G wireless networks are expected to be a mixture of network tiers of different sizes, transmit powers, backhaul connections, different radio access technologies (RATs) that are accessed by an unprecedented numbers of smart and heterogeneous wireless devices. This architectural enhancement along with the advanced physical communications technology such as high-order spatial multiplexing multiple-input multiple-output (MIMO) communications will provide higher aggregate capacity for more simultaneous users, or higher level spectral efficiency, when compared to the 4G networks. Radio resource and interference management will be a key research challenge in multi-tier and heterogeneous 5G cellular networks. The traditional methods for radio resource and interference management (e.g., channel allocation, power control, cell association or load balancing) in single-tier networks (even some of those developed for two-tier networks) may not be efficient in this environment and a new look into the interference management problem will be required.First, the article outlines the visions and requirements of 5G cellular wireless systems. Major research challenges are then highlighted from the perspective of interference management when the different network tiers share the same radio spectrum. A comparative analysis of the existing approaches for distributed cell association and power control (CAPC) is then provided followed by a discussion on their limitations for5G multi-tier cellular networks. Finally, a number of suggestions are provided to modifythe existing CAPC schemes to overcome these limitations.II. VISIONS AND REQUIREMENTS FOR 5G MULTI-TIERCELLULAR NETWORKS5G mobile and wireless communication systems will require a mix of new system concepts to boost the spectral and energy efficiency. The visions and requirements for 5G wireless systems are outlined below.·Data rate and latency: For dense urban areas, 5G networks are envisioned to enable an experienced data rate of 300 Mbps and 60 Mbps in downlink and uplink, respectively, in 95% of locations and time [2]. The end-to- end latencies are expected to be in the order of 2 to 5 milliseconds. The detailed requirements for different scenarios are listed in [2].·Machine-type Communication (MTC) devices: The number of traditional human-centric wireless devices with Internet connectivity (e.g., smart phones, super-phones, tablets) may be outnumbered by MTC devices which can be used in vehicles, home appliances, surveillance devices, and sensors.·Millimeter-wave communication: To satisfy the exponential increase in traffic and the addition of different devices and services, additional spectrum beyond what was previously allocated to 4G standard is sought for. The use of millimeter-wave frequency bands (e.g., 28 GHz and 38 GHz bands) is a potential candidate to overcome the problem of scarce spectrum resources since it allows transmission at wider bandwidths than conventional 20 MHz channels for 4G systems.·Multiple RATs: 5G is not about replacing the existing technologies, but it is about enhancing and supporting them with new technologies [1]. In 5G systems, the existing RATs, including GSM (Global System for Mobile Communications), HSPA+ (Evolved High-Speed Packet Access), and LTE, will continue to evolve to provide a superior system performance. They will also be accompanied by some new technologies (e.g., beyondLTE-Advanced).·Base station (BS) densification: BS densification is an effective methodology to meet the requirements of 5G wireless networks. Specifically, in 5G networks, there will be deployments of a large number of low power nodes, relays, and device-to-device (D2D) communication links with much higher density than today’s macrocell networks.Fig. 1 shows such a multi-tier network with a macrocell overlaid by relays, picocells, femtocells, and D2D links. The adoption of multiple tiers in the cellular networkarchitecture will result in better performance in terms of capacity, coverage, spectral efficiency, and total power consumption, provided that the inter-tier and intratier interferences are well managed.·Prioritized spectrum access: The notions of both trafficbased and tier-based Prioriti -es will exist in 5G networks. Traffic-based priority arises from the different requirements of the users (e.g., reliability and latency requirements, energy constraints), whereas the tier-based priority is for users belonging to different network tiers. For example, with shared spectrum access among macrocells and femtocells in a two-tier network, femtocells create ―dead zones‖ around them in the downlink for macro users. Protection should, thus, be guaranteed for the macro users. Consequently, the macro and femtousers play the role of high-priority users (HPUEs) and lowpriority users (LPUEs), respectively. In the uplink direction, the macrocell users at the cell edge typically transmit with high powers which generates high uplink interference to nearby femtocells. Therefore, in this case, the user priorities should get reversed. Another example is a D2D transmission where different devices may opportunistically access the spectrum to establish a communication link between them provided that the interference introduced to the cellular users remains below a given threshold. In this case, the D2D users play the role of LPUEs whereas the cellular users play the role of HPUEs.·Network-assisted D2D communication: In the LTE Rel- 12 and beyond, focus will be on network controlled D2D communications, where the macrocell BS performs control signaling in terms of synchronization, beacon signal configuration and providing identity and security management [3]. This feature will extend in 5G networks to allow other nodes, rather than the macrocell BS, to have the control. For example, consider a D2D link at the cell edge and the direct link between the D2D transmitter UE to the macrocell is in deep fade, then the relay node can be responsible for the control signaling of the D2Dlink (i.e., relay-aided D2D communication).·Energy harvesting for energy-efficient communication: One of the main challenges in 5G wireless networks is to improve the energy efficiency of the battery-constrained wireless devices. To prolong the battery lifetime as well as to improve the energy efficiency, an appealing solution is to harvest energy from environmental energy sources (e.g., solar and wind energy). Also, energy can be harvested from ambient radio signals (i.e., RF energy harvesting) with reasonable efficiency over small distances. The havested energy could be used for D2D communication or communication within a small cell. Inthis context, simultaneous wireless information and power transfer (SWIPT) is a promising technology for 5G wireless networks. However, practical circuits for harvesting energy are not yet available since the conventional receiver architecture is designed for information transfer only and, thus, may not be optimal for SWIPT. This is due to the fact that both information and power transfer operate with different power sensitivities at the receiver (e.g., -10dBm and -60dBm for energy and information receivers, respectively) [4]. Also, due to the potentially low efficiency of energy harvesting from ambient radio signals, a combination of different energy harvesting technologies may be required for macrocell communication.III. INTERFERENCE MANAGEMENT CHALLENGES IN 5GMULTI-TIER NETWORKSThe key challenges for interference management in 5G multi-tier networks will arise due to the following reasons which affect the interference dynamics in the uplink and downlink of the network: (i) heterogeneity and dense deployment of wireless devices, (ii) coverage and traffic load imbalance due to varying transmit powers of different BSs in the downlink, (iii) public or private access restrictions in different tiers that lead to diverse interference levels, and (iv) the priorities in accessing channels of different frequencies and resource allocation strategies. Moreover, the introduction of carrier aggregation, cooperation among BSs (e.g., by using coordinated multi-point transmission (CoMP)) as well as direct communication among users (e.g., D2D communication) may further complicate the dynamics of the interference. The above factors translate into the following key challenges.·Designing optimized cell association and power control (CAPC) methods for multi-tier networks: Optimizing the cell associations and transmit powers of users in the uplink or the transmit powers of BSs in the downlink are classical techniques to simultaneously enhance the system performance in various aspects such as interference mitigation, throughput maximization, and reduction in power consumption. Typically, the former is needed to maximize spectral efficiency, whereas the latter is required to minimize the power (and hence minimize the interference to other links) while keeping theFig. 1. A multi-tier network composed of macrocells, picocells, femtocells, relays, and D2D links.Arrows indicate wireless links, whereas the dashed lines denote the backhaul connections. desired link quality. Since it is not efficient to connect to a congested BS despite its high achieved signal-to-interference ratio (SIR), cell association should also consider the status of each BS (load) and the channel state of each UE. The increase in the number of available BSs along with multi-point transmissions and carrier aggregation provide multiple degrees of freedom for resource allocation and cell-selection strategies. For power control, the priority of different tiers need also be maintained by incorporating the quality constraints of HPUEs. Unlike downlink, the transmission power in the uplink depends on the user’s batt ery power irrespective of the type of BS with which users are connected. The battery power does not vary significantly from user to user; therefore, the problems of coverage and traffic load imbalance may not exist in the uplink. This leads to considerable asymmetries between the uplink and downlink user association policies. Consequently, the optimal solutions for downlink CAPC problems may not be optimal for the uplink. It is therefore necessary to develop joint optimization frameworks that can provide near-optimal, if not optimal, solutions for both uplink and downlink. Moreover, to deal with this issue of asymmetry, separate uplink and downlink optimal solutions are also useful as far as mobile users can connect with two different BSs for uplink and downlink transmissions which is expected to be the case in 5G multi-tier cellular networks [3].·Designing efficient methods to support simultaneous association to multiple BSs: Compared to existing CAPC schemes in which each user can associate to a singleBS, simultaneous connectivity to several BSs could be possible in 5G multi-tier network. This would enhance the system throughput and reduce the outage ratio by effectively utilizing the available resources, particularly for cell edge users. Thus the existing CAPCschemes should be extended to efficiently support simultaneous association of a user to multiple BSs and determine under which conditions a given UE is associated to which BSs in the uplink and/or downlink.·Designing efficient methods for cooperation and coordination among multiple tiers: Cooperation and coordination among different tiers will be a key requirement to mitigate interference in 5G networks. Cooperation between the macrocell and small cells was proposed for LTE Rel-12 in the context of soft cell, where the UEs are allowed to have dual connectivity by simultaneously connecting to the macrocell and the small cell for uplink and downlink communications or vice versa [3]. As has been mentioned before in the context of asymmetry of transmission power in uplink and downlink, a UE may experience the highest downlink power transmission from the macrocell, whereas the highest uplink path gain may be from a nearby small cell. In this case, the UE can associate to the macrocell in the downlink and to the small cell in the uplink. CoMP schemes based on cooperation among BSs in different tiers (e.g., cooperation between macrocells and small cells) can be developed to mitigate interference in the network. Such schemes need to be adaptive and consider user locations as well as channel conditions to maximize the spectral and energy efficiency of the network. This cooperation however, requires tight integration of low power nodes into the network through the use of reliable, fast andlow latency backhaul connections which will be a major technical issue for upcoming multi-tier 5G networks. In the remaining of this article, we will focus on the review of existing power control and cell association strategies to demonstrate their limitations for interference management in 5G multi-tier prioritized cellular networks (i.e., where users in different tiers have different priorities depending on the location, application requirements and so on). Design guidelines will then be provided to overcome these limitations. Note that issues such as channel scheduling in frequency domain, timedomain interference coordination techniques (e.g., based on almost blank subframes), coordinated multi-point transmission, and spatial domain techniques (e.g., based on smart antenna techniques) are not considered in this article.IV. DISTRIBUTED CELL ASSOCIATION AND POWERCONTROL SCHEMES: CURRENT STATE OF THE ARTA. Distributed Cell Association SchemesThe state-of-the-art cell association schemes that are currently under investigation formulti-tier cellular networks are reviewed and their limitations are explained below.·Reference Signal Received Power (RSRP)-based scheme [5]: A user is associated with the BS whose signal is received with the largest average strength. A variant of RSRP, i.e., Reference Signal Received Quality (RSRQ) is also used for cell selection in LTE single-tier networks which is similar to the signal-to-interference (SIR)-based cell selection where a user selects a BS communicating with which gives the highest SIR. In single-tier networks with uniform traffic, such a criterion may maximize the network throughput. However, due to varying transmit powers of different BSs in the downlink of multi-tier networks, such cell association policies can create a huge traffic load imbalance. This phenomenon leads to overloading of high power tiers while leaving low power tiers underutilized.·Bias-based Cell Range Expansion (CRE) [6]: The idea of CRE has been emerged as a remedy to the problem of load imbalance in the downlink. It aims to increase the downlink coverage footprint of low power BSs by adding a positive bias to their signal strengths (i.e., RSRP or RSRQ). Such BSs are referred to as biased BSs. This biasing allows more users to associate with low power or biased BSs and thereby achieve a better cell load balancing. Nevertheless, such off-loaded users may experience unfavorable channel from the biased BSs and strong interference from the unbiased high-power BSs. The trade-off between cell load balancing and system throughput therefore strictly depends on the selected bias values which need to be optimized in order to maximize the system utility. In this context, a baseline approach in LTE-Advanced is to ―orthogonalize‖ the transmissions of the biased and unbiased BSs in time/frequency domain such that an interference-free zone is created.·Association based on Almost Blank Sub-frame (ABS) ratio [7]: The ABS technique uses time domain orthogonalization in which specific sub-frames are left blank by the unbiased BS and off-loaded users are scheduled within these sub-frames to avoid inter-tier interference. This improves the overall throughput of the off-loaded users by sacrificing the time sub-frames and throughput of the unbiased BS. The larger bias values result in higher degree of offloading and thus require more blank subframes to protect the offloaded users. Given a specific number of ABSs or the ratio of blank over total number of sub-frames (i.e., ABS ratio) that ensures the minimum throughput of the unbiased BSs, this criterion allows a user to select a cell with maximum ABS ratio and may even associate with the unbiased BS if ABS ratio decreases significantly. A qualitative comparison amongthese cell association schemes is given in Table I. The specific key terms used in Table I are defined as follows: channel-aware schemes depend on the knowledge of instantaneous channel and transmit power at the receiver. The interference-aware schemes depend on the knowledge of instantaneous interference at the receiver. The load-aware schemes depend on the traffic load information (e.g., number of users). The resource-aware schemes require the resource allocation information (i.e., the chance of getting a channel or the proportion of resources available in a cell). The priority-aware schemes require the information regarding the priority of different tiers and allow a protection to HPUEs. All of the above mentioned schemes are independent, distributed, and can be incorporated with any type of power control scheme. Although simple and tractable, the standard cell association schemes, i.e., RSRP, RSRQ, and CRE are unable to guarantee the optimum performance in multi-tier networks unless critical parameters, such as bias values, transmit power of the users in the uplink and BSs in the downlink, resource partitioning, etc. are optimized.B. Distributed Power Control SchemesFrom a user’s point of view, the objective of power control is to support a user with its minimum acceptable throughput, whereas from a system’s point of view it is t o maximize the aggregate throughput. In the former case, it is required to compensate for the near-far effect by allocating higher power levels to users with poor channels as compared to UEs with good channels. In the latter case, high power levels are allocated to users with best channels and very low (even zero) power levels are allocated to others. The aggregate transmit power, the outage ratio, and the aggregate throughput (i.e., the sum of achievable rates by the UEs) are the most important measures to compare the performance of different power control schemes. The outage ratio of a particular tier can be expressed as the ratio of the number of UEs supported by a tier with their minimum target SIRs and the total number of UEs in that tier. Numerous power control schemes have been proposed in the literature for single-tier cellular wireless networks. According to the corresponding objective functions and assumptions, the schemes can be classified into the following four types.·Target-SIR-tracking power control (TPC) [8]: In the TPC, each UE tracks its own predefined fixed target-SIR. The TPC enables the UEs to achieve their fixed target-TABLE IQUALITATIVE COMPARISON OF EXISTING CELL ASSOCIATION SCHEMESFOR MULTI-TIER NETWORKSSIRs at minimal aggregate transmit power, assuming thatthe target-SIRs are feasible. However, when the system is infeasible, all non-supported UEs (those who cannot obtain their target-SIRs) transmit at their maximum power, which causes unnecessary power consumption and interference to other users, and therefore, increases the number of non-supported UEs.·TPC with gradual removal (TPC-GR) [9], [10], and [11]:To decrease the outage ra -tio of the TPC in an infeasiblesystem, a number of TPC-GR algorithms were proposedin which non-supported users reduce their transmit power[10] or are gradually removed [9], [11].·Opportunistic power control (OPC) [12]: From the system’s point of view, OPC allocates high power levels to users with good channels (experiencing high path-gains and low interference levels) and very low power to users with poor channels. In this algorithm, a small difference in path-gains between two users may lead to a large difference in their actual throughputs [12]. OPC improves the system performance at the cost of reduced fairness among users.·Dynamic-SIR tracking power control (DTPC) [13]: When the target-SIR requirements for users are feasible, TPC causes users to exactly hit their fixed target-SIRs even if additional resources are still available that can otherwise be used to achieve higher SIRs (and thus better throughputs). Besides, the fixed-target-SIR assignment is suitable only for voice service for which reaching a SIR value higher than the given target value does not affect the service quality significantly. In contrast, for data services, a higher SIR results in a better throughput, which is desirable. The DTPC algorithm was proposed in [13] to address the problem of system throughput maximization subject to a given feasible lower bound for the achieved SIRs of all users in cellular networks. In DTPC, each user dynamically sets its target-SIR by using TPC and OPC in a selective manner. It was shown that when the minimum acceptable target-SIRs are feasible, the actual SIRs received by some users can be dynamically increased (to a value higher than their minimum acceptabletarget-SIRs) in a distributed manner so far as the required resources are available and the system remains feasible (meaning that reaching the minimum target-SIRs for the remaining users are guaranteed). This enhances the system throughput (at the cost of higher power consumption) as compared to TPC. The aforementioned state-of-the-art distributed power control schemes for satisfying various objectives in single-tier wireless cellular networks are unable to address the interference management problem in prioritized 5G multi-tier networks. This is due to the fact that they do not guarantee that the total interference caused by the LPUEs to the HPUEs remain within tolerable limits, which can lead to the SIR outage of some HPUEs. Thus there is a need to modify the existing schemes such that LPUEs track their objectives while limiting their transmit power to maintain a given interference threshold at HPUEs. A qualitative comparison among various state-of-the-art power control problems with different objectives and constraints and their corresponding existing distributed solutions are shown in Table II. This table also shows how these schemes can be modified and generalized for designing CAPC schemes for prioritized 5G multi-tier networks.C. Joint Cell Association and Power Control SchemesA very few work in the literature have considered the problem of distributed CAPC jointly (e.g., [14]) with guaranteed convergence. For single-tier networks, a distributed framework for uplink was developed [14], which performs cell selection based on the effective-interference (ratio of instantaneous interference to channel gain) at the BSs and minimizes the aggregate uplink transmit power while attaining users’ desire d SIR targets. Following this approach, a unified distributed algorithm was designed in [15] for two-tier networks. The cell association is based on the effective-interference metric and is integrated with a hybrid power control (HPC) scheme which is a combination of TPC and OPC power control algorithms.Although the above frameworks are distributed and optimal/ suboptimal with guaranteed convergence in conventional networks, they may not be directly compatible to the 5G multi-tier networks. The interference dynamics in multi-tier networks depends significantly on the channel access protocols (or scheduling), QoS requirements and priorities at different tiers. Thus, the existing CAPC optimization problems should be modified to include various types of cell selection methods (some examples are provided in Table I) and power control methods with different objectives and interference constraints (e.g., interference constraints for macro cell UEs, picocell UEs, or D2Dreceiver UEs). A qualitative comparison among the existing CAPC schemes along with the open research areas are highlighted in Table II. A discussion on how these open problems can be addressed is provided in the next section.V. DESIGN GUIDELINES FOR DISTRIBUTED CAPCSCHEMES IN 5G MULTI-TIER NETWORKSInterference management in 5G networks requires efficient distributed CAPC schemes such that each user can possibly connect simultaneously to multiple BSs (can be different for uplink and downlink), while achieving load balancing in different cells and guaranteeing interference protection for the HPUEs. In what follows, we provide a number of suggestions to modify the existing schemes.A. Prioritized Power ControlTo guarantee interference protection for HPUEs, a possible strategy is to modify the existing power control schemes listed in the first column of Table II such that the LPUEs limit their transmit power to keep the interference caused to the HPUEs below a predefined threshold, while tracking their own objectives. In other words, as long as the HPUEs are protected against existence of LPUEs, the LPUEs could employ an existing distributed power control algorithm to satisfy a predefined goal. This offers some fruitful direction for future research and investigation as stated in Table II. To address these open problems in a distributed manner, the existing schemes should be modified so that the LPUEs in addition to setting their transmit power for tracking their objectives, limit their transmit power to keep their interference on receivers of HPUEs below a given threshold. This could be implemented by sending a command from HPUEs to its nearby LPUEs (like a closed-loop power control command used to address the near-far problem), when the interference caused by the LPUEs to the HPUEs exceeds a given threshold. We refer to this type of power control as prioritized power control. Note that the notion of priority and thus the need of prioritized power control exists implicitly in different scenarios of 5G networks, as briefly discussed in Section II. Along this line, some modified power control optimization problems are formulated for 5G multi-tier networks in second column of Table II.To compare the performance of existing distributed power control algorithms, let us consider a prioritized multi-tier cellular wireless network where a high-priority tier consisting of 3×3 macro cells, each of which covers an area of 1000 m×1000 m, coexists with a low-priority tier consisting of n small-cells per each high-priority macro cell, each。
外文翻译模板
大连交通大学信息工程学院毕业设计(论文)外文翻译学生姓名陈辉专业班级机械073班指导教师王凤彪职称讲师所在单位机械工程系教学部主任吕海霆完成日期 2011年4月15日Numerical Control SystemThe numerical control system is the digital control system abbreviation. By early is composed of hardware circuit is called hardware numerical control (Hard NC), after 1970, hardware circuit components gradually instead by the computer called for computer numerical control system.Computerized numerical control system is a system that is use computer control processing function to achieve numerical control system. CNC system according to the computer memory stored in the control program execution part or all, numerical control function, and is equipped with interface circuit and servo drive the special computer system.CNC system consists of NC program, input devices; output devices, computer numerical control equipment (CNC equipment), programmable logic controllers (PLC), the spindle and feed drive (servo) drive (including detection devices) and so on.The core of CNC system is equipment. By using the computer system with the function of software and PLC instead of the traditional machine electric device to make the system logic control more compact, its flexibility and versatility, reliability become more better, easy to implement complex numerical control function, use and maintenance can be more convenient, and it also has connected and super ordination machine and the remote communication function.At present, the numerical control system has variety of different forms; composition structure has its own characteristics. These structural features from the basic requirements of the initial system design and engineering design ideas. For example, the control system of point and continuous path control systems have different requirements. For the T system and the M system, there are also very different, the former applies to rotary part processing, the latter suitable for special-shaped the axially symmetrical parts processing. For different manufacturers, based on historical development factors and vary their complex factors, may also be thinking in the design is different. For example, the United States Dynapath system uses a small plate for easy replacement and flexible combination of the board; while Japan FANUC system is a large plate structure tends to make the system work in favor of reliability, make the system MTBF rate continues to increase. However, no matter what kind of system, their basic principle and structure are very similar.The numerical control system generally consists of three major components, namely the control system, servo system and position measuring system. Control procedures by interpolation operation work piece, issue control instructions to the servo drive system; servo drive system control instructions amplified by the servo motor-driven mechanical movement required; measurement system detects the movement of mechanical position or speed, and feedback to the control system, to modify the control instructions. These three parts combine to form a complete closed-loop control of the CNC system.Control system mainly consists of bus, CPU, power supply, memory, operating panel and display, position control unit, programmable logic controller control unit and datainput / output interface and so on. The latest generation of CNC system also includes a communication unit; it can complete the CNC, PLC's internal data communications and external high-order networks. Servo drive system including servo drives and motors. Position measuring system is mainly used grating, or circular grating incremental displacement encoder.CNC system hardware from the NC device, input / output devices, drives and machine logic control devices, electrical components, between the four parts through the I / O interface to interconnect.Numerical control device is the core of CNC system, its software and hardware to control the implementation of various CNC functions.The hardware structure of no device by CNC installations in the printed circuit board with infixing pattern can be divided into the big board structure and function module (small board) structure; Press CNC apparatus hardware manufacturing mode, can be divided into special structure and personal computer type structure; Press CNC apparatus in the number of microprocessor can be divided into single microprocessor structure and many microprocessor structure.(1)Large panel structure and function templates structure1) Large panel structurePanel structures CNC system CNC equipment from the main circuit board, position control panels, PC boards, graphics control panel, additional I / O board and power supply unit and other components. The main circuit board printed circuit board is big; the other circuit board is a small plate, inserted in the large printed circuit board slot. This structure is similar to the structure of micro-computer.2) Function templates structure(2)Single-microprocessor structure and mulct-microprocessor structure1) Single-microprocessor structureIn a single-microprocessor structure, only a microprocessor to focus on control, time-sharing deals with the various tasks of CNC equipment.2) melt-microprocessor structureWith the increase in numerical control system functions, CNC machine tools to improve the processing speed of a single microprocessor CNC system can not meet the requirement; therefore, many CNC systems uses a multi-microprocessor structure. If a numerical control system has two or more microprocessors, each microprocessor via the data bus or communication to connect, share system memory and common I / O interfaces, each processor sharing system Part of the work, which is multi-processor systems.CNC software is divided into application software and system software. CNC system software for the realization of various functions of the CNC system, the preparation of special software, also known as control software, stored in the computer EPROM memory. CNC Systems feature a variety of settings and different control schemes, and their system software in the structure and size vary widely, but generally include input data processing procedures, computing interpolation procedures, speed control procedures, management procedures and diagnostic procedures.(1)Input data processing proceduresIt receives input part program, the standard code, said processing instructions and datadecoding, data processing, according to the prescribed format for storage. Some systems also calculated to compensate, or interpolation operation and speed control for pre-computation. Typically, the input data processing program, including input, decoding and data processing three elements.(2)Computing interpolation proceduresCNC work piece processing system according to the data provided, such as curve type, start, end, etc. operations. According to the results of operations were sent to each axis feed pulse. This process is called interpolation operation. Feed drive servo system Impulsive table or by a corresponding movement of the tool to complete the procedural requirements of the processing tasks.Interpolation for CNC system is the side of the operation, while processing, is a typical real-time control, so the interpolation directly affects the speed of operation the machine feed rate, and should therefore be possible to shorten computation time, which is the preparation of interpolation Complements the key to the program.(3)Speed control proceduresSpeed control program according to the given value control the speed of operation of the frequency interpolation, in order to maintain a predetermined feed rate. Changes in speed is large, the need for automatic control of acceleration and deceleration to avoid speed drive system caused by mutations in step.(4)Management proceduresManagement procedures responsible for data input, data processing, interpolation processing services operations as the various procedures for regulation and management. Management process but also on the panel command, the clock signal, the interrupt caused by fault signals for processing.(5)Diagnostic proceduresDiagnostic features are found in the running system failure in a timely manner, and that the type of failure. Y ou can also run before or after the failure, check the system main components (CPU, memory, interfaces, switches, servo systems, etc.) function is normal, and that the site of failure.MachiningAny machining must have three basic conditions: machining tools, work piece and machining sports. Machining tool edge should be, the material must be rigid than the work piece. Different forms of tool structure and cutting movements constitute different cutting methods. Blade with a blade-shaped and have a fixed number of methods for cutting tools for turning, drilling, boring, milling, planning, broaching, and sawing, etc.; edge shape and edge with no fixed number of abrasive or abrasive Cutting methods are grinding, grinding, honing and polishing.Machining is the most important machinery manufacturing processing methods. Although the rough improve manufacturing precision, casting, forging, extrusion, powder metallurgy processing applications on widely, but to adapt to a wide range of machining,and can achieve high accuracy and low surface roughness, in Manufacturing still plays an important role in the process. Cutting metal materials have many classifications. Common are the following three kinds.By cutting process feature distinguishing characteristics of the decision process on the structure of cutting tools and cutting tools and work piece relative motion form. According to the technical characteristics of cutting can be divided into: turning, milling, drilling, boring, reaming, planning, shaping, slotting, broaching, sawing, grinding, grinding, honing, super finishing, polishing, gear Processing, the worm process, thread processing, ultra-precision machining, bench and scrapers and so on. By material removal rate and machining accuracy distinction can be divided into: ① rough: with large depth of cut, one or a few times by the knife away from the work cut out most or all allowances, such as rough turning, rough planning, Rough milling, drilling and sawing, etc., rough machining precision high efficiency low, generally used as a pre-processing, and sometimes also for final processing. ② Semi-finishing: General roughing and finishing as the middle between the process, but the work piece accuracy and surface roughness on the less demanding position, but also can be used as the final processing. ③ finishing: cutting with a fine way to achieve higher machining surface accuracy and surface quality, such as fine cars, fine planning, precision hinges, grinding and so on. General is the final finishing process. ④Finishing process: after the finish, the aim is to obtain a smaller surface roughness and to slightly improve the accuracy. Finishing processing allowance is small, such as honing, grinding, ultra-precision grinding and super finishing and so on. ⑤Modification process: the aim is to reduce the surface roughness, to improve the corrosion, dust properties and improve appearance, but does not require higher precision, such as polishing, sanding, etc. ⑥ultra-precision machining: aerospace, lasers, electronics, nuclear energy and other cutting-edge technologies that need some special precision parts, high accuracy over IT4, surface roughness less than Ra 0.01 microns. This need to take special measures to ultra-precision machining, such as turning mirror, mirror grinding, chemical mechanical polishing of soft abrasive.Distinguished by method of surface machining, the work piece is to rely on the machined surface for cutting tool and the work piece to obtain the relative motion. By surface methods, cutting can be divided into three categories. ①tip trajectory method: relying on the tip relative to the trajectory of the surface to obtain the required work piece surface geometry, such as cylindrical turning, planning surface, cylindrical grinding, with the forming surface, such as by turning mode. The trajectory depends on the tool tip provided by the cutting tool and work piece relative motion. ② forming tool method: short forming method, with the final work piece surface profile that matches the shape forming cutter or grinding wheel, such as processing a shaped surface. At this time forming part of the machine movement was replaced by the blade geometry, such as the shape of turning, milling and forming grinding forming and so on. The more difficult the manufacture of forming cutter, machine - clamp - work piece - tool formed by the process system can withstand the cutting force is limited, forming method is generally used for processing short shaped surface. ③generating method: also known as rotary cutting method, cutting tool and work piece during processing as a relatively developed into a campaign tool (or wheel) and the work piece instantaneous center line of pure rolling interaction between thetwo maintain a certain ratio between Is obtained by processing the surface of the blade in this movement in the envelope. Gear machining hobbling, gear shaping, shaving, honing, and grinding teeth (not including form grinding teeth), etc. are generating method processing.PLCEarly called the programmable logic controller PLC (Programmable Logic Controller, PLC), which is mainly used to replace the logic control relays. With the technology, which uses micro-computer technology, industrial control device function has been greatly exceeded the scope of logic control, therefore, such a device today called programmable logic controller, referred to as the PC. However, in order to avoid personal computer (Personal Computer) in the short confusion, it will be referred to as programmable logic controller PLC, plc since 1966, the U.S. Digital Equipment Corporation (DEC) developed there, the current United States, Japan, Germany, PLC Good quality and powerful.The basic structure of Programmable Logic ControllerA. PowerPLC's power in the whole system plays a very important role. If you do not have a good, reliable power system is not working, so the PLC manufacturers design and manufacture of power very seriously. General AC voltage fluctuations of +10% (+15%) range, you can not take other measures to PLC to connect directly to the AC line.B.Central processing unit (CPU)Central processing unit (CPU) is the central PLC control. It is given by the function of PLC system program from the programmer receives and stores the user program and data type; check the power supply, memory, I / O and timer alert status, and to diagnose syntax errors in the user program. When the PLC into run-time, first it scans the scene to receive the status of various input devices and data, respectively, into I / O image area, and then one by one from the user program reads the user program memory, after a shell and press Provisions of the Directive the result of logic or arithmetic operations into the I / O image area or data register. And the entire user program is finished, and finally I / O image area of the state or the output of the output register data to the appropriate output device, and so on to run until stopped.To further improve the reliability of PLC, PLC is also large in recent years constitutes a redundant dual-CPU system, or by three voting systems CPU. Thus, even if a CPU fails, the whole system can still work properly.C.MemoryStorage system software of memory called system program memory. Storage application software of memory called the user program memory.D.Input and output interface circuit1, the live input interface circuit by the optical coupling circuit and the computer input interface circuit, the role of PLC and field control of an interface for input channels.2, Field output interface circuit by the output data registers, interrupt request strobe circuit and integrated circuit, the role of PLC output interface circuit through the on-siteimplementation of parts of the output to the field corresponding control signal.E.Function moduleSuch as counting, positioning modules.munication moduleSuch as Ethernet, RS485, Prefab’s-DP communication module.数控系统数控系统是数字控制系统简称，英文名称为Numerical Control System，早期是由硬件电路构成的称为硬件数控（Hard NC），1970年代以后，硬件电路元件逐步由专用的计算机代替称为计算机数控系统。
毕业设计(论文)外文参考文献译文本
武汉工业学院毕业设计（论文）外文参考文献译文本2011届原文出处IBM SYSTEMS JOURNAL, VOL 35, NOS 3&4, 1996毕业设计(论文)题目音乐图像浏览器的设计与实现院（系）计算机与信息工程专业名称计算机科学与技术学生姓名郭谦学生学号070501103指导教师丰洪才译文要求：1、译文内容须与课题（或专业）有联系；2、外文翻译不少于4000汉字。
隐藏数据技术研究数据隐藏，是一种隐秘的数据加密形式，它将数据嵌入到数字媒体之中来达到鉴定，注释和版权保护的目的。
然而，这一应用却受到了一些限制：首先是需要隐藏的数据量，其次是在“主”讯号受到失真的条件影响之下，对于这些需隐藏数据的可靠性的需要。
举例来说，就是有损压缩以及对有损压缩来说数据遇到被拦截，被修改或被第三方移除等操作的免疫程度。
我们同时用传统的和新式技术来探究解决数据隐藏问题的方法并且对这些技术在以下三个方面的应用：版权保护，防止篡改，和增强型数据嵌入做出评估。
我们能非常方便地得到数字媒体并且潜在地改善了其可移植性，信息展现的效率，和信息呈现的准确度。
便捷的数据访问所带来的负面效果包括以下两点：侵犯版权的几率增加或者是有篡改或修改其中内容的可能性增大。
这项工作的目的在于研究知识产权保护条款、内容修改的相关指示和增加注解的方法。
数据隐藏代表了一类用于插入数据的操作，例如版权信息，它利用“主”信号能够感知的最小变化量来进入到各种不同形式的媒体之内，比如图像、声音或本文。
也就是说，嵌入的数据对人类观察者来说应该是既看不见也听不见的。
值得注意的是，数据隐藏虽然与压缩很类似，但与加密解密技术却是截然不同的。
它的目标不是限制或者管理对“主”信号的存取，而是保证被嵌入的数据依然未被破坏而且是可以恢复的。
数据隐藏在数字媒体中的两个重要应用就是提供版权信息的证明，和保证内容完整性。
因此，即使主讯号遭受诸如过滤、重取样，截取或是有损压缩等破坏行为，数据也应该一直在“主”信号中保持被隐藏的特点。
毕业设计外文翻译模板
本科生毕业设计（论文）外文翻译毕业设计（论文）题目：组合钻床动力滑台液压系统及电控系统设计外文题目： Drilling machine译文题目：组合钻床学生姓名：马莉莉专业：机械设计制造及其自动化0701班指导教师姓名：王洁评阅日期：正文内容小四号字，宋体，行距1.5倍行距。
The drilling machine is a machine for making holes with removal of chips and it is used to create or enlarge holes. There are many different types of drilling machine for different jobs, but they can be basically broken down into two categories.The bench drill is used for drilling holes through raw materials such as wood, plastic and metal and gets its name because it is bolted to bench for stability so that larger pieces of work can be drilled safely. The pillar drill is a larger version that stands upright on the floor. It can do exactly the same work as the bench drill, but because of its size it can be used to drill larger pieces of materials and produce bigger holes. Most modern drilling machines are digitally automated using the latest computer numerical control (CNC) technology.Because they can be programmed to produce precise results, over and over again, CNC drilling machines are particularly useful for pattern hole drilling, small hole drilling and angled holes.If you need your drilling machine to work at high volume, a multi spindle drill head will allow you to drill many holes at the same time. These are also sometimes referred to as gang drills.Twist drills are suitable for wood, metal and plastics and can be used for both hand and machine drilling, with a drill set typically including sizes from 1mm to 14mm. A type of drill machine known as the turret stores tools in the turret and positions them in the order needed for work.Drilling machines, which can also be referred to as bench mounted drills or floor standing drills are fixed style of drills that may be mounted on a stand or bolted to the floor or workbench. A drilling machine consists of a base, column, table, spindle), and drill head, usually driven by an induction motor.The head typically has a set of three which radiate from a central hub that, when turned, move the spindle and chuck vertically, parallel to the axis of the column. The table can be adjusted vertically and is generally moved by a rack and pinion. Some older models do however rely on the operator to lift and re clamp the table in position. The table may also be offset from the spindles axis and in some cases rotated to a position perpendicular to the column.The size of a drill press is typically measured in terms of swing which can be is defined as twice the throat distance, which is the distance from the centre of the spindle to the closest edge of the pillar. Speed change on these drilling machines is achieved by manually moving a belt across a stepped pulley arrangement.Some drills add a third stepped pulley to increase the speed range. Moderndrilling machines can, however, use a variable-speed motor in conjunction with the stepped-pulley system. Some machine shop drilling machines are equipped with a continuously variable transmission, giving a wide speed range, as well as the ability to change speed while the machine is running.Machine drilling has a number of advantages over a hand-held drill. Firstly, it requires much less to apply the drill to the work piece. The movement of the chuck and spindle is by a lever working on a rack and pinion, which gives the operator considerable mechanical advantage.The use of a table also allows a vice or clamp to be used to position and restrain the work. This makes the operation much more secure. In addition to this, the angle of the spindle is fixed relative to the table, allowing holes to be drilled accurately and repetitively.Most modern drilling machines are digitally automated using the latest computer numerical control (CNC) technology. Because they can be programmed to produce precise results, over and over again, CNC drilling machines are particularly useful for pattern hole drilling, small hole drilling and angled holes.Drilling machines are often used for miscellaneous workshop tasks such as sanding, honing or polishing, by mounting sanding drums, honing wheels and various other rotating accessories in the chuck. To add your products click on the traders account link above.You can click on the links below to browse for new, used or to hire a drilling machine.Drilling machines are used for drilling, boring, countersinking, reaming, and tapping. Several types are used in metalworking: vertical drilling machines, horizontal drilling machines, center-drilling machines, gang drilling machines, multiple-spindle drilling machines, and special-purpose drilling machines.Vertical drilling machines are the most widely used in metalworking. They are used to make holes in relatively small work-pieces in individual and small-lot production; they are also used in maintenance shops. The tool, such as a drill, countersink, or reamer, is fastened on a vertical spindle, and the work-piece is secured on the table of the machine. The axes of the tool and the hole to be drilled are aligned by moving the workpiece. Programmed control is also used to orient the workpiece and to automate the operation. Bench-mounted machines, usually of the single-spindle type, are used to make holes up to 12 mm in diameter, for instance, in instrument-making.Heavy and large workpieces and workpieces with holes located along a curved edge are worked on radial drilling machines. Here the axes of the tool and the hole to be drilled are aligned by moving the spindle relative to the stationary work-piece.Horizontal drilling machines are usually used to make deep holes, for instance, in axles, shafts, and gun barrels for firearms and artillery pieces.Center-drilling machines are used to drill centers in the ends of blanks. They are sometimes equipped with supports that can cut off the blank before centering, and in such cases they are called center-drilling machines. Gang drilling machines with more than one drill head are used to produce several holes at one time. Multiple-spindle drilling machines feature automation of the work process. Such machines can be assembled from several standardized, self-contained heads with electric motors and reduction gears that rotate the spindle and feed the head. There are one-, two-, and three-sidedmultiple-spindle drilling machines with vertical, horizontal, and inclined spindles for drilling and tapping. Several dozen such spindles may be mounted on a single machine. Special-purpose drilling machines, on which a limited range of operations is performed, are equipped with various automated devices.Multiple operations on workpieces are performed by various combination machines. These include one- and two-sided jig boring machines,drilling-tapping machines (usually gang drilling machines with reversible thread-cutting spindles), milling-type drilling machines and drilling-mortising machines used mainly for woodworking, and automatic drilling machines.In woodworking much use is made of single- and multiple-spindle vertical drilling machines, one- and two-sided, horizontal drilling machines (usually with multiple spindles), and machines equipped with a swivel spindle that can be positioned vertically and horizontally. In addition to drilling holes, woodworking machines may be used to make grooves, recesses, and mortises and to remove knots.英文翻译指导教师评阅意见。
(完整版)_毕业设计英文翻译_及格式
毕业设计(论文)英文翻译题目专业班级姓名学号指导教师职称200年月日The Restructuring of OrganizationsThroughout the 1990s, mergers and acquisitions a major source of corporate restructuring, affecting millions of workers and their families. This form of restructuring often is accompanied by downsizing. Downsizing is the process of reducing the size of a firm by laying off or retiring workers early. The primary objectives of downsizing are similar in U.S. companies and those in other countries:●cutting cost,●spurring decentralization and speeding up decision making,●cutting bureaucracy and eliminating layers of especially they did five years ago. One consequence of this trend is that today’s managers supervise larger numbers of subordinates who report directly to them. In 1990, only about 20 percent of managers supervise twelve or more people and 54 percent supervised six or fewer.Because of downsizing, first-line managers quality control, resources, and industrial engineering provide guidance and support. First-line managers participate in the production processes and other line activities and coordinate the efforts of the specialists as part of their jobs. At the same time, the workers that first-line managers supervise are less willing to put up with authoritarian management. Employees want their jobs to be more creative, challenging, fun, and satisfying and want to participate in decisions affecting their work. Thus self-managed work teams that bring workers and first-line managers together to make joint decisions to improve the way they do their jobs offer a solution to both supervision and employee expectation problems. When you ’t always the case. Sometimes entire divisions of a firm are simply spun off from the main company to operate on their own as new, autonomous companies. The firm that spun them off may then become one of their most important customers or suppliers. That AT&T “downsized” the old Bell Labs unit, which is now known as Lucent Technologies. Now, rather than - return is free to enter into contracts with companies other than AT&T. this method of downsizing is usually called outsourcing.Outsourcing means letting other organizations perform a needed service andor manufacture needed parts or products. Nike outsources the production of its shoes to low-cost plants in South Korea and China and imports the shoes for distribution in North America. These same plants also ship shoes to Europe and other parts of Asia for distribution. Thus today’s managers face a new challenge: t o plan, organize, lead, and control a company that may as a modular corporation. The modularcorporation is most is most common in three industries: apparel, auto manufacturing, and electronics. The most commonly out-sourced function is production. By out sourcing production, a company can switch supplier best suited to a customer’s needs.Decisions about what to outsource and what to keep in- to contract production to another company is a sound business decision to contract production to another company is a sound business decision, at least for U.S. manufacturers. It appears to the unit cost of production by relieving the company of some overhead, and it frees the company to allocate scarce resources to activities for which the company examples of modular companies are Dell Computer, Nike, Liz Claiborne fashions, and ship designer Cyrix.As organizations downsize and outsource functions, they become flatter and smaller. Unlike the behemoths of the past, the new, smaller firms are less like autonomous fortresses and more like nodes in a net work of complex relationships. This approach, called the network form of organization, involves establishing strategic alliances among several entities.In Japan, cross-ownership and alliances among firms－called keiretsu－both foreign and U.S. auto parts producers. It also owns 49 percent of Hertz, the car rental company that is also a major customer. Other alliances include involvement in several research consortia. In the airline industry, a common type of alliance is between an airline and an airframe manufacture. For example, Delta recently agreed to buy all its aircraft from Boeing. Boeing Airlines. Through these agreements, Boeing guarantees that it will be able to sell specified models of its aircraft and begin to adapt their operations to the models they will be flying in the future. Thus both sides expect to reap benefits from these arrangements for many years.Networks forms of organizations are prevalent in access to the universities and in small, creative organizations. For example, the U.S. biotechnology industry is characterized by network of relationships between new biotechnology firms dedicated to research and new products development and established firms in industries that can use these new products, such as pharmaceuticals. In return for sharing technical information with the larger firms, the smaller firms gain access to their partners’ resources for product testing, marketing, and distribution. Big pharmaceutical firms such as Merk or Eli Lily gain from such partnerships because the smaller firms typically development cycle in the larger firms.Being competitive increasingly requires establishing and managing strategic alliances with other firms. In a strategic alliance, two or more firms agree to cooperate in a venture that is expected to benefit both firms.企业重组整个20世纪90年代中，合并和收购一直是企业重组的主要起源，影响着千百万的工人和他们的家庭。
毕业设计(论文)外文资料翻译〔含原文〕【范本模板】
南京理工大学毕业设计（论文）外文资料翻译教学点: 南京信息职业技术学院专业：电子信息工程姓名：陈洁学号:014910253034外文出处：《Pci System Architecture 》(用外文写)附件： 1.外文资料翻译译文；2。
外文原文。
附件1：外文资料翻译译文64位PCI扩展1.64位数据传送和64位寻址：独立的能力PCI规范给出了允许64位总线主设备与64位目标实现64位数据传送的机理。
在传送的开始，如果回应目标是一个64位或32位设备，64位总线设备会自动识别.如果它是64位设备,达到8个字节(一个4字）可以在每个数据段中传送。
假定是一串0等待状态数据段。
在33MHz总线速率上可以每秒264兆字节获取(8字节／传送＊33百万传送字／秒），在66MHz总线上可以528M字节／秒获取.如果回应目标是32位设备,总线主设备会自动识别并且在下部4位数据通道上（AD［31:：00］)引导，所以数据指向或来自目标。
规范也定义了64位存储器寻址功能。
此功能只用于寻址驻留在4GB地址边界以上的存储器目标。
32位和64位总线主设备都可以实现64位寻址。
此外，对64位寻址反映的存储器目标（驻留在4GB地址边界上）可以看作32位或64位目标来实现。
注意64位寻址和64位数据传送功能是两种特性,各自独立并且严格区分开来是非常重要的。
一个设备可以支持一种、另一种、都支持或都不支持。
2.64位扩展信号为了支持64位数据传送功能，PCI总线另有39个引脚。
●REQ64＃被64位总线主设备有效表明它想执行64位数据传送操作.REQ64＃与FRAME＃信号具有相同的时序和间隔。
REQ64#信号必须由系统主板上的上拉电阻来支持.当32位总线主设备进行传送时，REQ64#不能又漂移。
●ACK64#被目标有效以回应被主设备有效的REQ64＃(如果目标支持64位数据传送）,ACK64#与DEVSEL＃具有相同的时序和间隔（但是直到REQ64＃被主设备有效，ACK64#才可被有效）.像REQ64＃一样，ACK64#信号线也必须由系统主板上的上拉电阻来支持。
毕业设计(论文)外文资料翻译(学生用)
毕业设计外文资料翻译学院：信息科学与工程学院专业：软件工程姓名： XXXXX学号： XXXXXXXXX外文出处： Think In Java (用外文写)附件： 1.外文资料翻译译文；2.外文原文。
附件1：外文资料翻译译文网络编程历史上的网络编程都倾向于困难、复杂，而且极易出错。
程序员必须掌握与网络有关的大量细节，有时甚至要对硬件有深刻的认识。
一般地，我们需要理解连网协议中不同的“层”（Layer）。
而且对于每个连网库，一般都包含了数量众多的函数，分别涉及信息块的连接、打包和拆包；这些块的来回运输；以及握手等等。
这是一项令人痛苦的工作。
但是，连网本身的概念并不是很难。
我们想获得位于其他地方某台机器上的信息，并把它们移到这儿；或者相反。
这与读写文件非常相似，只是文件存在于远程机器上，而且远程机器有权决定如何处理我们请求或者发送的数据。
Java最出色的一个地方就是它的“无痛苦连网”概念。
有关连网的基层细节已被尽可能地提取出去，并隐藏在JVM以及Java的本机安装系统里进行控制。
我们使用的编程模型是一个文件的模型；事实上，网络连接（一个“套接字”）已被封装到系统对象里，所以可象对其他数据流那样采用同样的方法调用。
除此以外，在我们处理另一个连网问题——同时控制多个网络连接——的时候，Java内建的多线程机制也是十分方便的。
本章将用一系列易懂的例子解释Java的连网支持。
15.1 机器的标识当然，为了分辨来自别处的一台机器，以及为了保证自己连接的是希望的那台机器，必须有一种机制能独一无二地标识出网络内的每台机器。
早期网络只解决了如何在本地网络环境中为机器提供唯一的名字。
但Java面向的是整个因特网，这要求用一种机制对来自世界各地的机器进行标识。
为达到这个目的，我们采用了IP（互联网地址）的概念。
IP以两种形式存在着：(1) 大家最熟悉的DNS（域名服务）形式。
我自己的域名是。
所以假定我在自己的域内有一台名为Opus的计算机，它的域名就可以是。
外文文献翻译封面格式及要求(模版)
毕业论文外文文献翻译院年级专业：2009级XXXXXXXXXXX 姓 名：学 号：附 件：备注：(注意：备注页这一整页的内容都不需要打印，看懂了即可）1.从所引用的与毕业设计（论文）内容相近的外文文献中选择一篇或一部分进行翻译(不少于3000实词)；2。
外文文献翻译的装订分两部分，第一部分为外文文献；第二部分为该外文文献的中文翻译，两部分之间用分页符隔开.也就是说，第一外文文献部分结束后，使用分页符，另起一页开始翻译。
3。
格式方面，外文文献的格式，除了字体统一使用Times new roman 之外，其他所有都跟中文论文的格式一样.中文翻译的格式,跟中文论文的格式一样。
(注意:备注页这一整页的内容都不需要打印，看懂了即可，定稿后,请删除本页.）范文如下:注意,下面内容每一部份均已用分页符分开了，如果用本模板,请将每一模块单独删除,直接套用到每一模板里面，不要将全部内容一次性删除。
【Abstract】This paper has a systematic analysis on outside Marco—environment of herbal tea beverage industry and major competitors of brands inside the herbal tea market。
Based onthe theoretic framework, this paper takes WONG LO KAT and JIA DUO BAO herbal tea as an example, and researches the strategy on brand positioning and relevant marketing mix of it. Through analysis on the prevention sense of WONG LO KAT herbal tea, it was positioned the beverage that can prevent excessive internal heat in body, a new category divided from the beverage market。
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信工学院毕业设计外文
翻译封面
Document serial number【NL89WT-NY98YT-NC8CB-NNUUT-NUT108】
毕业设计外文资料翻译
专业名称网络工程
班级学号
学生姓名吕帅
指导教师胡硕
填表日期 2015 年 04 月 02 日
Cryptography isone ofthe maintraditional technology andinformation security technology,it is theShannoninformation theory andcryptography theory andtechnology based on thedigital content protection,theuse ofencryptionmethod to
complete,i.e.themultimediadata fileis encrypted into ciphertextafter the
release,theillegal attackerappearsin the transmission processcannot obtainconfidentialinformation from thetext,so as to achievethe purpose ofcopyright protection andinformation security.Butthis does not completely solve the problem: the spread ofanencrypted filebecause it is notcomprehensibleand hinderthe multimedia information;on the other hand,through themultimedia informationencryptionis easy to causethe attacker'sattention and curiosity,andthere isthe possibility of cracking,and when theinformation isreceivedanddecrypted,theencryptionthe documentandthe document,will no longer be protected,not spared frompiracy.In other
words,cryptographycan protectthe transmissionofcontent,and the contentoncedecryptionwill no longer have theprotection.Therefore,there is an urgent need for areplacementorsupplement thecryptographytechnology,itevencan continue to protect thecontent is decryptedincontent.In this way,people put forward thenewconcept ofdigital watermarking,information hiding.Digital watermark isa new direction in thefield of information security technology,is anewtechnologyto protectcopyright and authentication source andintegrality in theopen network environment,the creation ofinformation andpersonal logocreatorthrough digitalwatermarking system toembed the watermarkcan not be perceivedbypeoplein themedia,peoplecan not perceiveon the face ofthe watermark,onlyspecial detector orcomputer softwarethatcan detect thedigital watermarkhidden.。