Extending an open media-streaming platform to support Differentiated Services
S. Zoi, P. Papageorgioy, D. Loukatos, P. Stathopoulos, and N. Mitrou
National Technical University of Athens, ECE Department
Heroon Polytechneioy 9
GR-15773 Zografou, Greece
Abstract – In this paper, architectural extensions for enhancing an open media-streaming platform with differentiated services mechanisms are studied, implemented, and experimentally evaluated. Towards this end, an appropriate layering is adopted in order to enable definition of Quality of Service (QoS) specifications and their mapping to network parameters during transmission. Furthermore, a component dedicated to the off-line study of quality requirements is specified and integrated into the QoS aware platform. This component enables to preview the effects of quality violations on media streams, before they are transmitted to the network, by simulating packet losses/delays during the packetization process. Based on this component, a suitable quality metric is introduced for video streams, which is sensitive both to spatial and temporal distortion effects and can be easily applied to other types of streams, or to groups of related streams (e.g. synchronized audio-video). The aforementioned extensions are implemented on the open source MPEG4IP platform. The applicability of certain QoS policies is experimentally evaluated over a laboratory-based DiffServ testbed. In this case, QoS specifications are mapped to DiffServ compliant Type of Service (ToS) values during transmission. Experiments are conducted with an MPEG-4 encoded video stream under different network configurations, QoS policies, and error resilience mechanisms. The performance of the stream is evaluated based on the proposed quality metric.
Keywords: Differentiated services, streaming platform, QoS specifications, quality metric, MPEG4IP, ToS marking, DiffServ testbed
1 INTRODUCTION
State-of-the-art multimedia technology gives the potential to author complex networked multimedia applications, composed of multiple media streams (e.g. audio, video, virtual reality, images) [MPEG-4 Systems] [URL SMIL]. However, the deployment of Quality of Service (QoS) mechanisms to such applications is still very limited even though network level QoS frameworks do exist, such as the Differentiated Services (DiffServ) [Blake] and the Integrated Services frameworks [Braden]. This is mainly because the definition of portable QoS specifications that map application level QoS into network level parameters is still an open issue.
Although several application level QoS frameworks have appeared so far, e.g. MPEG-4 Delivery Multimedia Integration Framework – DMIF [Marques] and Microsoft’s Winsock 2 API [URL Microsoft], studies concerning the definition and experimental evaluation of QoS mechanisms for multimedia streams are usually restricted to single stream traces [Fitzek], and simulated networks [Marques] [Bocheck]. This is due to the fact that those frameworks focus on QoS parameters defined at network level (e.g. packet loss rate, packet delay and delay variation) and do not take into consideration application semantics. Furthermore, other popular Application Programming Interfaces (APIs), like those of Java, do not even have QoS extensions.
What is needed is the ability of the application to define its own quality parameters, in such a way that perceived quality is also captured. These parameters should be incorporated into the real application environment in the form of portable QoS specifications that are independent of the underlying network service. Furthermore, metrics able to capture these application quality parameters and map them to quantifiable quantities are also necessary.
In this paper, architectural extensions for enhancing a media-streaming platform with differentiated services QoS mechanisms are studied, implemented, and experimentally evaluated. Towards this end, an appropriate layering is adopted in order to enable definition of QoS specifications and their mapping to network parameters during transmission. Furthermore, a component dedicated to the off-line study of quality requirements is specified and integrated into the enhanced platform. This component enables to preview the effects of quality violations on media streams, before they are transmitted to the network, by simulating packet losses/delays during the packetization process. Based on this component, a suitable quality metric is introduced for video streams, which is sensitive both to spatial and temporal distortion effects and can be easily applied to other types of streams, as well as to groups of related streams (e.g. synchronized audio-video). The aforementioned extensions are implemented on the open source MPEG4IP platform. The applicability of certain QoS policies is experimentally evaluated over a laboratory-based DiffServ testbed. In this case QoS specifications are mapped to DiffServ compliant Type of Service (ToS) values during transmission. Experiments are conducted with an MPEG-4 encoded video stream under different network configurations, QoS policies, and error resilience mechanisms. The performance of the stream is evaluated based on the proposed quality metric.
The rest of the paper is organized as follows. Section 2 presents related work concerning service differentiation mechanisms for multimedia streams, quality metrics and QoS enhanced multimedia environments. Section 3 discusses architectural extensions required for making a real application platform QoS aware. Section 4 explains how these extensions are implemented on the MPEG4IP platform in order to support packet service differentiation. In section 5, different QoS policies applied on an MPEG-4 encoded video stream are experimentally evaluated on the QoS aware platform, over Best Effort and DiffServ configurations. Finally, section 6 provides conclusions and directions for further work.
2 RELATED WORK
2.1 Service differentiation mechanisms for multimedia streams
The Differentiated Services (DiffServ) framework [Blake] supports the differentiation of packets, not only belonging to different competitive streams, but also within the same stream, therefore defining several priority levels. This is achieved by marking the Type of Service (ToS) byte [Stevens] of each packet header. This feature can be exploited by applying packet differentiation policies to media streams based on their semantics, in order to achieve graceful quality degradation, as described among others in [Masala], [Miska], [Tan], [Tian], [Kim] and [Mohaparta].
MPEG-4 [URL MPEG] is a promising standard for delivering mixed media services over a wide range of networks. In MPEG-4 encoding, high compression is achieved at the cost of low error resistance and therefore, several optional error resilience mechanisms are foreseen by the standard [MPEG-4 Visual], such as resynchronization and data partitioning. Resynchronization is based on the incorporation of special markers into the bitstream for localizing errors and regaining synchronization between the encoder and the decoder. Data partitioning is based on the separation of shape and motion data from texture data, for each macroblock, thus allowing one to be recovered even if the other is lost. The object-oriented nature of MPEG-4 content structuring and other advanced encoding features provide flexibility as to robust network transmission. For example, in [Cellatoglu] object-oriented MPEG-4 video coding is exploited to implement dynamic prioritisation schemes by varying bit allocation among different video objects. In [Worrall] a technique for altering MPEG-4 encoding parameters to increase error robustness is presented, based on the fact that frames with high motion degree are often more sensitive to errors than the others. In [Worrall Febri] a method for prioritizing data partitioned MPEG-4 video for transmission over mobile networks is examined over simulated GPRS data channels.
2.2 Quality metrics for multimedia applications
At user level, usually, perceived quality is evaluated by using subjective methods [MOS]. These methods require human viewers to rate the quality of the received stream; this subjective assessment, however, can be costly, time-consuming and difficult to give quantifiable results.
In the case of audio a set of methods of quality evaluation have been proposed and some of them are standardized [PESQ] [PEAQ]. These methods take into consideration human psychoacoustics and relate them with phenomena that come from errors, losses, variable delays, encoding distortions etc. In this way, an objective quality assessment methodology gives results, which are analogous of a subjective methodology (e.g. MOS).
In the case of video, many researchers evaluate the quality of the pictures based on the Peak Signal-to-Noise Ratio (PSNR) [URL PSNR] of the resulting frame difference between the original sequence and the decoded one. The PSNR, which was initially defined for analog video signals, is able to accurately measure and assess analog impairments to the video signal. However, with the introduction and development of digital technologies, visually noticeable artifacts are being manifested in ways that are different from analog artifacts.
2.3 QoS frameworks for real application environments
The problem of defining frameworks for QoS–aware multimedia applications has not been exhausted yet, although several studies have appeared in the literature ([Chang], [Wichadakul]). The framework proposed in [Chang] relies upon a dynamic QoS monitoring scheme. This scheme is based on ATM specific network feedback mechanisms, in order to guarantee synchronization requirements of SMIL presentations. In [Wichadakul] the “QCompiler” programming framework is presented and experimentally evaluated for quality aware ubiquitous multimedia applications. Four layers are defined: (1) a high-level application specification layer allowing the user to specify application quality requirements, (2) a metadata compilation layer which compiles the quality requirements of layer 1 to a quality specification, (3) a binding layer which prepares a quality specification to be executed in a specific environment and (4) a run-time metadata execution layer, which uses the bound quality specification, to manage and control a quality aware multimedia application.
3 ARCHITECTURAL EXTENSIONS FOR ENHANCING A REAL APPLICATION PLATFORM
WITH DIFFERENTIATED SERVICES MECHANISMS
The layering architecture described in subsection 2.2 is adopted in this work and is suitably adjusted for the case of differentiated services (see figure1).
At the high-level application specification layer user quality levels are defined based on stream subsets, for example High, Medium, and Low, as illustrated in figure 2. The definitions of these subsets can be based on the service differentiation mechanisms described in subsection 2.1.
Figure 1 – The QoS aware layering architecture
Figure 2 - Different user quality levels
At the Metadata Compilation layer, high-level stream quality requirements are incorporated into lower-level metadata descriptions, produced during the encoding process. This is mainly the case for pre-encoded streams. In the case of real-time encoded and transmitted streams (live streams), these requirements are transferred in real-time from the encoding to the transmission layer. This can be achieved, for example, by mapping every quality level to an arithmetic value. According to its contribution to quality every part of the produced bitstream, corresponding to a semantic entity (e.g. video frame, motion vector, video object), is associated with one of these values, during encoding. The metadata descriptors related to quality, as well as the arithmetic values assigned to each video entity can be thought of as the QoS specification , for pre-encoded and live streams correspondingly.
The Binding layer takes as input the QoS specification and prepares it to be executable in a specific environment (e.g. by mapping a network service interface to a QoS enhanced socket system call). In the case of DiffServ, packet differentiation and assignment to the different DiffServ classes is achieved through marking of the ToS byte of the packet header, with a value corresponding to a Per Hop Behavior (PHB) [Black
], which in turn corresponds to a QoS level.
In the Run-time Metadata Execution layer the metadata descriptions are parsed and different QoS levels are assigned to different network classes, e.g. through DiffServ compliant ToS marking performed by the streaming server during the packetization process. In the case of live streams the streaming server uses the arithmetic descriptors assigned to each packet during the packetization process, to mark each of them with a ToS value corresponding to a quality level.
4 EXTENDING THE MPEG4IP MEDIA-STREAMING PLATFORM TO SUPPORT SERVICE
DIFFERENTIATION
features
4.1 Existing
The MPEG4IP project [URL MPEG4IP] is an open-source (C/C++ based) platform, mainly developed by Cisco Inc. incorporating additional open source tools from other parties. It provides a standards-based, end-to-end platform for encoding, decoding, and streaming, over the UDP/RTP protocol stack, MPEG-4 audio/video streams. The client side mainly comprises the player and the content decoders, while the server side comprises the following components:
A toolkit for off-line encoding of MPEG-4 compatible streams (Divx [URL divx] or ISO MPEG-4 simple profile
video [Bocheck] and AAC audio [MPEG-4 Audio]). In this package a utility for incorporating hint information inside the mp4 file metadata description is also included (mp4creator).
An application (mp4live) for capturing, real-time encoding, and streaming video and audio content.
A streaming server, in this case, the open-source Apple’s Darwin Streaming Server (DSS) [URL darwin].
4.2 Error resilience mechanisms implementation
In the current releases of MPEG4IP no error resilience mechanisms are included and a single network packet loss results in the player discarding the whole video frame. Therefore, resynchronization and data partitioning mechanisms (see section 2), have been implemented to enable a VOP to be decoded even under the presence of lost packets.
The implementation of resynchronization is based on the concept of video packets. A video packet, which is an independently decodable portion of data (see [MPEG-4 Visual]), is based on periodic resynchronization markers within the bitstream. The length of a video packet is not determined based on the number of macroblocks but rather on the number of bits contained in this packet.
Data partitioning, which improves error localization, is based on the separation of motion and texture data, for each macroblock, within a video packet. This method requires placing a resynchronization marker between these two parts of data. If texture information is lost, then this method exploits motion data for error concealment, which means that motion information is used for motion compensating the previously decoded VOP.
Towards the implementation of the above mechanisms on the MPEG4IP platform the first important step is to select a suitable size for the video packet. This decision depends both on encoding parameters (e.g. encoding rate) and on the underlying network service (e.g. Best Effort or Differentiated Services). Generally it is preferable that no more than one video packet are put in one network packet. On the other hand, motion and texture data should be placed in different packets for the sake of better protection. This enables, for example, in the case of a DiffServ network, to apply a different service priority to the motion and texture data. For example, for the video which will be used as reference in the experiments (encoded at 500kbps) texture data produced during encoding fits to more than 3 network packets, depending on the percentage of Intra-encoded macroblocks. Motion data fits to about 2 network packets of size about 1460 bytes (which is defined as the maximum packet size of the network interface). In this sense, 2 video packets could be defined for each frame. However, in terms of implementation, due to variable length encoding it is difficult to know beforehand the size of motion vectors and coefficients. Therefore the video packet was decided to contain the whole frame.
Furthermore, suitable markers are placed in the bitstream so that the decoder knows which macroblock is being processed. Also, because motion data are separated for every macroblock and are identifiable, the loss or distortion of any network packets does not lead to discarding the whole frame, but only to the distortion of macroblocks corresponding to the lost packets. In order to implement this functionality certain modifications and enhancements are necessary both at the encoder, and at the decoder side.
4.3 The differentiated services aware architecture
4.3.1 The high-level application specification layer
In this layer perceived quality is classified to levels based on different patterns of QoS violations. Towards this end, a quality study component has been developed inside the MPEG4IP platform. With this, QoS violation effects (e.g. losses, delays) can be simulated and previewed on a media stream (or groups of streams) before this is transmitted to the network. This is achieved on a packet basis, by delaying or preventing a packet from entering the output network interface, in a fully controllable way, based on the payload of the packet (e.g. flags, motion vectors, coefficients). In this way, effects of QoS violations can be related with semantic entities of the stream and stream relations (e.g. synchronization). These deliberate QoS violations can be configured to correspond to realistic conditions, such as bursty losses and delays, which may cause several consecutive frames to be discarded. The results in perceived quality can be viewed in a standalone network configuration. In this way, user level quality can be studied in two levels:
Level 1 – Subjective quality
Distortions caused by deliberate QoS violations can be observed by real users based on a standardized methodology of subjective quality assessment, such as MOS [MOS]. Within this context it is possible to study error propagation within a stream (or a group of related streams), while controllable QoS violations contribute towards quantifiable results.
For example, figures 3and4illustrate quality degradation observed in a pre-encoded video stream, in the following scenarios:
SCENARIO 1 (Leftmost column): The 5th packet of the first I frame is lost.The absence of error resilience results in discarding the whole first I frame (black frame). The rest of this column shows how the absence of this frame affects the sequence of P frames, till the 2nd I frame.
SCENARIO 2 (Leftmost column): The last packet of the first I frame is lost. Due to error resilience absence, again the whole first I frame is discarded, and therefore, quality degrades in the same way as in SCENARIO1.
SCENARIO 3 (Middle column): The5th packet of the first I frame is lost. An error localization mechanism based on resynchronization markers [MPEG-4 Visual] enables the decoder to decode this frame, even though the part corresponding to the lost coefficients is incomprehensible.
SCENARIO 4 (Rightmost column):The last packet of the first I frame is lost. Again, due to the error localization mechanism this frame is decoded and a much smaller part is incomprehensible.
SCENARIO 5: The last packet of the 3rd P frame is lost. Due to a data partitioning mechanism [MPEG-4 Visual] implemented for P frames, quality degradation is less severe than in the non-error resilient case. Specifically, in the error resilient case no motion vectors are lost, except for some coefficients, and this leads to a better compensation-estimation of the next P frames.
Other more complex patterns of packet losses (and delays) can also be studied within this context towards defining user quality levels (see subsection 2.1).
Figure 3 - Quality degradation for scenarios 1 to 4
Figure 4 - Quality degradation for scenario 5
SCENARIOS 1&2SCENARIO
3SCENARIO 4
SCENARIO 5
Level 2 – Stream semantics quantification
In a first attempt to quantify spatial effects the PSNR metric has been implemented within the quality study component. Figure 5 illustrates the results obtained for scenarios 1 to 5. The darker line corresponds to the error resilient stream, while the lighter line corresponds to the non-error resilient stream. The horizontal axis gives the frame number, while the vertical axis gives the PSNR value obtained for each frame.
Figure 5 – PSNR results for scenarios 1&3, 2&4, 5
The benefit of applying error resilience mechanisms is obvious resulting in higher PSNR values for each frame.
4.3.2 The metadata compilation layer and the binding layer
For the creation of QoS specifications two cases are examined, that of live and pre-encoded video streams.
4.3.2.1 Live video streams
The mp4live application is capable of capturing , encoding and transmitting MPEG-4 video/audio streams over the UDP/RTP protocol stack, in real time. In order to enhance this application with packet differentiation extensions, a dedicated marking component was implemented. This component is capable of differently labelling parts of the produced bitstream with arithmetic values corresponding to different quality levels, according to the contribution to quality. These values will be assigned to the corresponding packets as ToS values by the binding layer, during packetization. This concept is illustrated in figure 6 for the case of a data partitioned video stream.
Figure 6 - The marking component
In terms of implementation, a pointer (curr)holds fields of the currently encoded VOP, as well as other information produced during encoding. This pointer is exploited by marking component, together with the QoS specifications of the encoded data contained within the VOP. The QoS specifications are given to the marking component in the form of arithmetic values. This component is responsible for mapping them to a set of DiffServ compliant packet TOS values, based on the selected marking policy. Parameters for selecting a packet marking policy are different for different mechanisms of subsection 2.1. For example, a packet marking policy can be defined for unequal error protection of the stream by assigning, for example, different service priorities to motion and texture information in a data-partitioned stream [MPEG-4 Visual]. Such an algorithm is illustrated in figure 7 (it is also the case described in figure 6).
Figure 7 – A ToS marking algorithm for a data-partitioned stream
Other more advanced marking policies can be defined based on object extraction with video segmentation algorithms. The objects of interest (e.g. moving persons in a video conference application) can be assigned higher service priority.
4.3.2.2 Pre-encoded streams
In this case, the media stream is encoded off-line and the DSS server is used to packetize and transmit it over the network. Because the server is unaware of the MPEG-4 payload, the packetization process is realized based on metadata descriptions, which are incorporated into the media file during encoding and describe media data by reference. In MPEG4IP this is done with the mp4creator utility. The metadata format is according to [MPEG-4 Systems].
Metadata structuring is tree-like and is based on the concept of atoms. The general structure of the MP4 file is illustrated in figure 8.
Figure 8 - The mp4 file structure
The mdat atom abstracts the structure holding the actual media data. The moov is an atom whose sub-atoms define the metadata for a presentation. Every media track has its own timeline, samples (e.g. frames) and properties. One or more sample descriptions can be defined based on how the sample must be decoded. The mp4 file, also, describes how to synchronize the timelines of the tracks and the aggregate properties of the tracks. Hint tracks contain instructions for the streaming server on how to packetize media track data for transmission, e.g. based on an RFC as RFC 3016 in MPEG4IP [Kikuchi].
The MPEG4IP platform provides an API, referred to as MP4 library, for creating and modifying MP4 files as defined by [MPEG-4 Systems]. To accommodate applications that need access to information not otherwise available via the API there are file and track level generic get and set property routines that use arbitrary string property names. Also, a set of utilities is provided to inspect the metadata information created with every encoded MP4 file, such as the MP4Dump application.
This API is exploited for incorporating stream QoS specifications, which are based on stream semantics, into the metadata descriptions. Specifically, within the hint track information every RTP packet is described by a set of fields, giving for example, its size and its offset from the VOP start. A new field needs to be inserted corresponding to the quality level each packet is assigned at, depending on its payload (e.g. motion or texture data in the data partitioning case). Then the DSS packet-marking component reads from the hint track the QoS specifications and maps them to DiffServ compliant packet TOS values. This procedure is illustrated in figure 9.
Figure 9 – Mapping of QoS specifications to ToS values
In this way, the marking algorithms described in subsection 2.1 can be incorporated into the metadata descriptions. 4.3.3 The run-time metadata execution layer
Towards propagating QoS specifications to the network level the platform has been enhanced with ToS packet marking mechanisms, by exploiting the setsockopt() function of the socket networking API. DiffServ compliant packet marking is performed by setting the six bits of the Differentiated Service (DS) byte to the appropriate DS CodePoint value, corresponding to Assured Forwarding (AF) [Heinanen ] classes AF11 (0x28), AF12 (0x30) and AF13 (0x38).
4.4 The need for new quality metrics
It becomes apparent from subsection 4.2.1 that packet level metrics (e.g. % packet loss rate) cannot give an accurate estimation of the final perceived quality, as it is depicted in the aforementioned cases, since the loss of only one packet results in completely different perceived quality samples. Therefore, metrics able to quantify stream distortions by capturing stream semantics are necessary.
In the case of video, spatial and temporal effects of losses on frames are of interest to map user perceived quality. Spatial effects can be quantified based on metrics such as PSNR or on decoding statistics (e.g. percentage of coefficients or motion vectors successfully decoded). However, temporal effects can neither be captured by PSNR alone, nor by the total amount of frame losses, as different patterns of frame losses (consecutive or sparse) result in different quality levels. Therefore, a more descriptive metric capturing also temporal effects is introduced.
As indicated in [Mohapatra], in the case of Internet telephony, the perceived quality after bursty packet losses is often worse than when the occurrences of these losses are adequately spaced. To address this problem, the authors use a finite horizon QoS criterion called (m,k)-firm guarantee which was first proposed in [Hamdaoui]. A real-time audio stream is said to have an (m,k)-firm guarantee requirement if m out of any k consecutive packets in the stream (assuming that one packet contains one audio frame) must meet their respective QoS requirements. The probability of less than m out of any k consecutive packets meeting their respective requirements is then used as a QoS metric. Based on this concept, a similar metric is introduced in [Loukatos] to quantify patterns of delay variation violations to audio streams.
In the case of video streams, the (m, k) criterion is meaningless at packet level. On the contrary it is meaningful at frame level, as the frame is the entity mostly perceived by human eye. Therefore, in order to indicate the pattern of distortions/losses experienced by the video sequence the (m, k) criterion can be defined as the distortion/loss of m out of k consecutive frames within the video stream. Correspondingly, the probability of more than m out of any k consecutive frames, not satisfying a certain quality threshold (which means the frame is lost or severely distorted) is then used as a QoS metric giving more information about patterns of frame “gaps”. The abovementioned quality level threshold can be defined as a PSNR threshold value (or another spatial quality metric under which spatial quality is considered unacceptable or under which the frame is discarded). The definition of this threshold can be different for various quality levels and can be determined based on subjective metrics, such as MOS.
Within this context, the (m, k) metric for scenarios 1 to 3 is given in figure10. Value 12 has been selected as the PSNR threshold, with k having the value of 10. The horizontal line (at the level of 100) corresponds to scenarios 1 & 2, where, for any group of 10 consecutive frames, the number of violations (i.e. the number of consecutive frames exhibiting a PSNR value less than 12) is at least 10. The second curve corresponds to scenario 3, where, for any group of 10 consecutive frames, the probability of having more than 3 consecutive violations is 0. The third curve corresponds to scenario 3, where for no group of 10 consecutive frames experiences any violations. These results are presented here for the purpose of indicating the capability of the (m, k) metric to clearly discriminate between the various video quality levels. In general, the selection of the threshold value is indicative and directly related to the user’s perception and the buffer size of the client application.
Figure 10 – The (m, k) metric as applied for scenarios 1 & 2, 3, and 4.
The above metric, together with the ability to study QoS violations with the quality study component can assist in evaluating the performance of different packet marking policies, as will be shown in section 5. Moreover, because this metric is highly parametric and is applied at semantic entity level (e.g. frame level in the case of video) it can be easily extended to other kinds of streams, based on their semantics, as well as to related streams (e.g. synchronized audio-video), based on the semantics of the relation.
5 EXPERIMENTAL EVALUATION OF THE ENHANCED PLATFORM ON A DIFFSERV
LABORATORY TESTBED
In this section a set of experiments are conducted with the differentiated services enhanced MPEG4IP platform, in order to evaluate the applicability of different packet marking policies.
5.1 Experiments platform topology
A QoS extended version of the MPEG4IP package, DSS , a PC generating competing traffic and a DiffServ enabled router were used for the experiments (see figure 11).
Figure 11 - The experimental platform
The platform was based on Linux PCs and a Linux router. Built in traffic control and DiffServ [Floyd] capabilities of Linux were exploited. The AF PHB was implemented at the router using a Random Early Detection (RED) [URL XML] queue. Traffic capturing tools such as tcpdump, ttt and other custom post-processing tools were used to capture and visualize the results.
In this section, the performance of a video stream, encoded with and without error resilience, is experimentally evaluated under Best Effort and DiffServ configurations. The encoding parameters of this stream are: Frame rate 10fps, Resolution 176 X 144, Encoding rate 500kbps. Another competing video stream is used, encoded at 120 kbps. The first one produces average rate of 502,5 kbps, while the second 123,7 kbps. The traffic profile of the two video streams is given in figure 12.
Figure 12 - Traffic profile of the two competing video streams
5.1.1 The Best Effort case settings
In the Best Effort configuration two cases are examined, one without incorporating error resilience mechanisms, and another incorporating error resilience mechanisms, which are based on resynchronisation markers, for I frames and data partitioning for P frames.
DSS is configured not to mark video packets with a ToS value, and therefore packets are directed to a Best Effort queue, which is controlled by Random Early Detection (RED), configured with the following set of parameters: limit 60KB, min 15KB, max 45KB, dropping probability 0.4. The allocated bandwidth is 600kbps. The video stream of interest shares this queue with the abovementioned competing video stream.
Because of the absence of marking policy, packet losses are expected to be randomly distributed among I and P frames, motion and texture data, while in the error resilient case the stream is expected to be more protected. The relative results are exposed in subsection 5.1.3.
5.1.2 The DiffServ case settings
In this case, a Class Based Queuing policy is implemented and configured at a bandwidth level of 600kbps. For each one of the classes being allocated (AF11 and AF12), a RED control queue is defined and configured with the following set of parameters:
For AF11: limit 60KB, min 15KB, max 45KB, dropping probability 0.02
For AF12: limit 60KB, min 15KB, max 45KB, dropping probability 0.04
In the case where error resilience is absent, I frames of the two competing videos are directed towards the AF11 class, while P frames towards the AF12 class. In the other case (with error resilience), the packets corresponding to motion information of data-partitioned P frames are marked by the DSS server with a higher service priority, and are therefore directed to the AF11 class along with I frames. The relative results are exposed in subsection5.1.3.
5.1.3 Comparison of results
The multiplexed video traffic was injected to the network, under the configurations described in subsections 5.1.1 and 5.1.2. Experimental results based on queuing statistic log files and on the (m,k) metric are presented.
Regarding the queue statistics (see table 1), the overall behavior of the system is as expected. In the cases where error resilience is applied (2 and 4) we have slightly heavier total packets losses comparing to the case where error resilience is not applied (case 2: 3,02% and case 4: 2,22% comparing with cases 1: 2,46% and case 3: 1,19%) This is explained by the fact that the error resilient stream features packets of slightly greater size thus having greater losses but with the advantage of much better performance in losses. In the DiffServ scenario the packets that are classified to the AF11 PHB are protected in any case. Moreover, when error resilience is introduced more packets are classified to the AF11 instead of the AF12 PHB. This however, does not imply that more packets are given better priority, since also the packets of the completive traffic are proportionally assigned greater priority.
Queue metrics/
Experiment Total pkts
sent Total pkts dropped (pkts/%) AF11 (sent, dropped,%) AF12 (sent, dropped,%)
1. BE without
resilience 11620 286 2,46%
2. BE with resilience
12021 364
3,02% 3. DiffServ without
resilience
10525 147 1,39% 895 0 0% 9683 147 1,51% 4. DiffServ with resilience 11629 257
2,22% 4744 0 0% 6961 257 3,69%
Table 1 – Queue statistics
For each one of the above four cases, the respective log file, containing the PSNR values calculated for the 500 kbps video stream, was used as input for the (m,k) metric evaluation mechanism. The corresponding results are shown in figure 13. Two different PSNR threshold values have been selected: 20 (left part of figure) and 25 (right part of figure). In both cases, Best Effort without error resilience experiences more violations. Best Effort with error resilience as well as DiffServ without error resilience experience medium quality results. This is due to the fact that in both a packet protection mechanism has been incorporated. When both mechanisms are present (one sensitive to ToS packet field value and another sensitive to frame type and motion/texture packet payload) the results become much better.
Figure 13 -
Quality metric results for threshold values 20 (left) and 25 (right) respectively.
6 CONCLUSIONS AND FURTHER WORK
In this paper, architectural extensions for enhancing an open streaming platform with differentiated service mechanisms are studied, implemented on the MPEG4IP platform, and experimentally evaluated over a DiffServ testbed. Towards this end, an appropriate layering is adopted in order to enable definition of QoS specifications and their mapping to network parameters during transmission. Furthermore, a component dedicated to the off-line study of quality requirements is specified and integrated into the QoS aware platform. Based on this component, a suitable quality metric is introduced for video streams, which is sensitive both to spatial and temporal distortion effects and can be easily applied to other types of streams. Experiments are conducted with an MPEG-4 encoded video stream under different network configurations, QoS policies, and error resilience mechanisms. The performance of the stream is evaluated based on the proposed quality metric.
Several directions for further work can be built on the work presented. More sophisticated packet-marking policies for unequal protection based on stream semantics, such as objects extracted with video segmentation algorithms [Cellatoglu] will be explored. In this context, new video quality metrics will be defined in assistance with the quality study component to capture block/object based distortion effects, which is not possible with PSNR.. Towards this end, more work is also required on the association of such QoS levels with subjective quality metrics [MOS]. Furthermore, multi-stream application scenarios with synchronization requirements will be studied within such a QoS framework, especially as far as qualitative and quantitative QoS guarantees are concerned [Chang]. New metrics will need to be explored for capturing delay effects and synchronization requirements. The use of metadata descriptions for defining portable QoS specifications will also be explored within this QoS framework based on content description technologies, such as XML [URL XML]. Experimentation so far has been done for specific scenarios and more work is needed to generalize the results and provide general operational rules, as far as network configuration parameters are concerned.
7 REFERENCES
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《运动控制系统》课程设计报告 时间 2014.10 _ 学院自动化 _ 专业班级自1103 _ 姓名曹俊博 __ 学号 41151093 指导教师潘月斗 ___ 成绩 _______
摘 要 本课程设计从直流电动机原理入手，建立V-M双闭环直流调速系统，设计双闭环直流调速系统的ACR和ASR结构，其中主回路采用晶闸管三相桥式全控整流电路供电，触发器采用KJ004触发电路，系统无静差；符合电流超调量σi≤5%；空载启动到额定转速超调量σn≤10%。并详细分析系统各部分原理及其静态和动态性能，且利用Simulink对系统进行各种参数给定下的仿真。 关键词：双闭环；直流调速；无静差；仿真 Abstract This course is designed from DC motor, establish the principles of V-M double closed loop DC speed control system design, the double closed loop dc speed control system and the structure, including ACR ASR the main loop thyristor three-phase bridge type all control the power supply and trigger the rectifier circuit KJ004 trigger circuit, the system without the static poor; Accord with current overshoots sigma I 5% or less; No-load start to the rated speed overshoot sigma n 10% or less. And detailed analysis of the system principle and the static and dynamic performance, and the system of simulink to various parameters set simulation. Key Words：double closed loop；DC speed control system；without the static poor；simulation
1、SDN是什么？ SDN(Software Defined Network)即软件定义网络，是一种网络设计理念。网络硬件可以集中式软件管理，可编程化，控制转发层面分开，则可以认为这个网络是一个SDN网络。SDN 不是一种具体的技术，不是一个具体的协议，而是一个思想，一个框架，只要符合控制和转发分离的思路就可以认为是SDN. 2、传统网络面临的问题？ 1）传统网络部署和管理非常麻烦，网络厂商杂，设备类型多，设备数量多，命令行不一致2）流量全局可视化难 3）分布式架构中，当网络发生震荡时，网络收敛过程中，有可能出现冗余的路径通告信息4）网络流量的剧增，导致底层网络的体积膨胀、压力增大；网络体积越大的话，需要收敛的时间就越长 5）想自定义设备的转发策略，而不是网络设备里面的固定好的转发策略 -------->sdn网络可以解决的问题 3、SDN的框架是什么 SDN框架主要由，应用层，控制层，转发层组成。其中应用层提供应用和服务（网管、安全、流控等服务），控制层提供统一的控制和管理（协议计算、策略下发、链路信息收集），转发层提供硬件设备（交换机、路由器、防火墙等）进行数据转发、 4、控制器 1）控制器概述 在整个SDN实现中，控制器在整个技术框架中最核心的地方控制层，作用是上接应用，下接设备。在SDN的商业战争中，谁掌握了控制器，或者制定了控制器的标准，谁在产业链条中就最有发言权 2）控制器功能 南向功能支撑：通过openflow等南向接口技术，对网络设备进行管控，拓扑发现，表项下
发，策略指定等 北向功能：目前SDN技术中只有南向技术有标准文案和规范，而北向支持没有标准。即便如此，控制器也需要对北向接口功能进行支持，REST API,SOAP,OSGI,这样才能够被上层的应用调用 东西向功能支持：分布式的控制器架构，多控制器之间如何进行选举、协同、主备切换等3）控制器的种类 目前市场上主要的控制器类型是：opendaylight （开发语言Java），Ryu(开发语言python), FloodLihgt(开发语言Java)等等 5、opendaylight（ODL）控制器介绍 ODL拥有一套模块化、可插拔灵活地控制平台作为核心，这个控制平台基于Java开发，理论上可以运行在任何支持Java的平台上，从Helium版本开始其官方文档推荐的最佳运行环境是最新的Linux（Ubuntu 12.04+）及JVM1.7+。 ODL控制器采用OSGi框架，OSGi框架是面向Java的动态模型系统，它实现了一个优雅、完整和动态的组件模型，应用程序（Bundle）无需重新引导可以被远程安装、启动、升级和卸载，通过OSGi捆绑可以灵活地加载代码与功能，实现功能隔离，解决了功能模块可扩展问题，同时方便功能模块的加载与协同工作。自Helium版本开始使用Karaf架构，作为轻量级的OSGi架构，相较于早前版本的OSGi提升了交互体验和效率，当然其特性远不仅仅于此。 ODL控制平台引入了SAL（服务抽象层），SAL北向连接功能模块，以插件的形式为之提供底层设备服务，南向连接多种协议，屏蔽不同协议的差异性，为上层功能模块提供一致性服务，使得上层模块与下层模块之间的调用相互隔离。SAL可自动适配底层不同设备，使开发者专注于业务应用的开发。 此外，ODL从Helium开始也逐渐完成了从AD-SAL（Application Driven Service Abstraction Layer）向MD-SAL（Model Driven Service Abstraction Layer）的演进工作，早前的AD-SAL，ODL控制平台采用了Infinispan技术，In?nispan是一个高扩展性、高可靠性、键值存储的分布式数据网格平台，选用Infinispan来实现数据的存储、查找及监听，用开源网格平台实现controller的集群。MD-SAL架构中采用Akka实现分布式messageing。 6、ODL的总体框架 ODL控制器主要包括开放的北向API，控制器平面，以及南向接口和协议插件。北向API 有OSGI和REST两类，同一地址空间应用使用OSGI类，而不同地址空间的应用则使用REST 类。OSGI是有状态的连接，有注册机制，而rest是无状态链接。上层应用程序利用这些北
产品市场前景预测分析报告： 产品技术水平 产品市场占有率分析 年来，我国电感器工业经济呈现出良好的发展态势，然而，随着市场规模的不断扩大，吸引了大量投资者进入，我国电感器企业的竞争环境正在发生急剧变化，随着对外开放和各地招商引资步伐的加快，巨大的市场需求也吸引着国外企业的进入。 年来，随着智能手机、智能家电、车载电子等领域的异军突起，电感器行业迎来新的发展巅峰期。根据中国电子元件行业协会信息中心《2011年中国电子元件产业集萃》披露，到2015年电感器销售额将增长至190亿元。 电感器如此庞大的市场前景令人心动不已，而对于广大的磁性元器件企业来说，要想抢占市场占有率，选择高性能磁芯材料成为关注的焦点之一。由于受电感器小型化的发展需要所限，磁芯材料需要具备有较高的磁导率、低的矫顽力、高的电阻率等。目前常用的磁芯材料有硅钢、铁氧体、非晶合金、超微晶、精密合金、磁粉芯等，由于不同磁性材料所做出来的磁芯不同，电感性能也各不相同，市场竞争力也就有了云泥之别。如何衡量每种材料的优缺点，为不同电感器选择性能最高的原材料，提高产品的竞争力，是所有工程师追求的目标。 主要是你们的磁通量做的好，磁芯材质好 高频电感器需求和产能日涨 在高频电子设备中，印制电路板上一段特殊形状的铜皮也可以构成一个电感器，通常把这种电感器称为印制电感或微带线。在智能系列产品的接受度和使用度大幅提高的现代社会，高频电感器的产能也随之高涨。 日前，日本村田制作所将扩大用于智能手机及平板终端等小型通信产品的高频电感器的产能，这一计划的实施主要是为了应对市场需求的扩大。另外，该公司还打算从2012年10月开始在冈山村田制作所生产面向大众消费市场的0603尺寸电感器产品。由此，两工厂的合计产能将提高至2011年10月的约4.6倍、2012年4月的约1.8倍。这一被扩大生产规模的高频电感器采用名为“厚膜印刷方式”的自主技术生产。该技术通过采用厚膜胶的光刻方式形成微细布线图案，可实现小型化及高Q值。 在工业电子和数据系统中，负载点电源的需求量大增，为大功率、小尺寸的电感带来了发展机遇。据了解，TDK的电感器销售额同比增长了27%，带动了TDK整体业务的增长。而这种增长在TDK分销商的销售业绩中得到了印证，小型电感器的市场需求量在不断增长，加上电感器生产厂商不断增加产品的附加值，这些都为小型电感器提供了成长空间。因此，在现货市场上，小型电感产品的市场份额呈现上升态势。 随着电子产品小型化的发展，电感器的体积已减小到物理极限。未来电感器的发展方向是集成化，电感器将与其它分立器件一起组合成复杂模块，为客户提供便于使用的完整系统。技术未突破前仍以小型化分立器件为主，要实现集成化还有一段距离。小型化将会是大部分电子设备的方向，我们已经看到了触屏手机、液晶电视、平板电脑的轻薄化趋势，因此，电感器作为电路系统中不可缺少的组件，轻薄小型、高效集成是必然走向。然而，在目前的技术水平以及原材料成本限制下，集成化的实现恐怕还需要一定的时日。
11级电气工程与自动化专业《运动控制系统》基本要求（2014-05-23） 第一章 绪论 了解本课程的研究内容。 第二章 （转速单）闭环控制的直流调速系统 1、 了解V （SCR ）--M 、PWM--M 两种主电路方案及其特点（2.1节、P16、P97--98、笔记）； 2、 他励（或永磁）直流电动机三种数学模型及转换，解耦模型中I do ~U d 环节的处理（P27--28、笔记）； 3、 稳态性能指标中D 、S 间关系及适用范围（2.2.1节、P29--30、笔记）； 4、 转速单闭环直流调速系统组成原理、特点及适用范围（P2 5、笔记）； 5、 带电流截至负反馈的转速单闭环直流调速系统的组成原理、特点（笔记、2.5.2节）。 第三章 转速、电流反馈控制的直流调速系统 1、 双闭环直流调速系统的组成原理（主要指：V —M 不可逆调速系统、PWM-M 调速系统）、特点，符合实际的系统数学模型，静（稳）态参数的整定及计算（P60、P59--6 2、笔记）； 2、 ASR 、ACR 的作用（P65）； 3、 典1、典2系统的特点、适用范围、参数整定依据（3.3.2节、笔记）； 4、 基于工程设计法的ASR 、ACR 调节器参数整定方法（P77--78、3.3.3节、例3-1、3-2、笔记）； 5、 理解ASR 退饱和时的（阶跃响应）转速超调量等时域指标算式（P86--88、笔记）； 6、 系统分别在正常恒流动态、稳态阶段，及机械堵转故障、转速反馈断开故障下的（新稳态）物理量计算； 7、 M 、T 、M/T 三种数字测速方法及特点（2.4.2节、笔记）； 8、 了解了解M/T 数字测速的技术实现方法、系统控制器的技术实现方法（P82-85、笔记）。 第四章 可逆控制和弱磁控制的直流调速系统 1、 PWM--M 可逆直流调速系统组成原理及特点（4.1节，笔记） 2、 V （SCR ）--M 可逆主电路中的环流概念、类型、特点（P103--104、笔记）； 3、 常用的晶闸管－直流电动机可逆调速系统组成原理及特点（4.2.2节，图4-1 4、图4-1 5、4.2.3节）。 第五章 基于稳态模型的异步电动机调速系统 1、 异步电动机定子调压调速的机械特性簇与特点，转速闭环调压调速系统组成原理及适用范围（5.1--5.2节）； 2、 软起动器的作用及适用条件（5.2.4节）； 3、 异步电动机变压变频调速的基本协调控制关系（一点两段）及其依据（5.3.1节）； 4、 异步电动机四种协调控制的特点，各自的机械特性簇、特点及比较（5.3.2节--5.3.3节、笔记）； 5、 SPWM 、CFPWM 、SVPWM 变频调速器组成原理与特点，及其中各环节的作用（5.4节）； 6、 了解基于转差频率控制的转速闭环变频变压调速系统的基本原理（5.6节）。 第六章 基于动态模型的异步电动机调速系统 1、 交流电动机坐标变换的作用，矢量控制（VC ）的基本思想、特点（6.6、6.7、笔记）； 2、 异步电动机VC 系统的一般组成原理（图6-20）； 3、 了解各种具体的VC 系统组成方案，理解转子磁链直接与间接定向控制的区别（6.6. 4、6.6.6节、笔记）； 4、 异步电动机直接转矩控制（DTC ）系统的基本原理及特点（6.7.3节），DTC 与VC 的比较（6.8节）。 第七章 绕线转子异步电动机双馈调速系统 1、 绕线转子异步电动机次同步串级调速主电路及其工作原理，()S f β=公式及特点（7.2.1节、笔记）； 2、 绕线转子异步电动机双闭环次同步串级调速系统组成原理；起动、停车操作步骤；（7.5、7.6、7.4.3节、笔记）。 第八章 同步电动机变压变频调速系统 1、 正弦波永磁同步电动机（PMSM ）矢量控制系统组成原理，0sd i =时的转矩公式（8.4.3节）； 2、 具有位置、速度闭环的正弦波永磁同步电动机（伺服）矢量控制系统组成原理（图8-26、27扩展、笔记）。 第九章 伺服系统 1、 位置伺服系统的典型结构（开环、半闭环、闭环、混合闭环）及特点（笔记、9.1.2）； 2、 位置伺服系统的三种运行方式、位置伺服系统的三种方案；（笔记、9.3.2--9.3.4） 3、 数字伺服系统中电子齿轮的作用（笔记）； 4、 数字式位置、速度伺服系统的指令形式（笔记）。 *** 考试须知---要点提示： （1）无证件者不能考试；（2）未交卷者中途不得离场；（3）严禁带手机到座位，操作手机者按作弊论处。 附：答疑地点（2-216）、时间：（1）2014-6-6，13:00--15:00；（2）2014-6-7，8:00--11:00，13:00--15:00。
企业产品市场前景分析报告 产品是企业价值的体现，是企业的立身之本、效益之源；市场是企业产品得以有效流通的渠道，是企业产品得以有效生存的基础。成功企业人士常说“没有倒闭的行业，只有衰退的企业；没有落后的市场，只有淘汰的产品。”优秀的企业创造出优质的产品，优质的产品才能在市场上畅通无阻，使市场得以有效地优化。我公司秉承客户至上、质量第一、诚信务实的市场经营理念，不断根据市场需求、客户需要，进行市场调整，优化产品质量，提高企业在市场上的信誉度和竞争力。 我公司自从创建以来，就时时紧跟市场步伐，优化市场资源配置，贴近客户需求，为广大消费者服务。不仅围绕市场开发出了“太合”牌系列产品，而且还扩大了市场范围、提高了市场占有率，有效地保证了市场供给，并深受广大客户与消费者欢迎和信赖。 公司坚持立足国内市场，努力开拓国际业务的经营策略。先后在全国主要的省市、自治区、直辖市上海、武汉、杭州、广州、重庆、昆明、贵阳、深圳等城市设立了自己的办事处，企业已形成了自己的较为完善的销售网络，并在这些销售网络的基础上优化对广大客户及消费者的服务体系。在“求实敬业、团结创新”的企业精神感召下，经过近几年来的不断探索和不懈努力，公司逐步走出一条优化产品生产、增强市场竞争、扩大用户需求的市场开拓之路。产品畅销全国二十多个省、市、自治区、直辖市，
市场占有率逐年攀升。 公司在健全市场网络和完善服务体系的同时，也扩大了产品销售量和市场占有率。企业年产值及销售收入均达到1.4亿元人民币以上，日销售额约120余万元人民币，在国内市场占有率也逐步提高。立足实际辉煌，展望前景美好。 公司在未来的发展中将以国外市场为方向，努力为企业创造出口条件，使产品走向海外。在以后的发展道路上，公司仍以国内市场为基础，继续扩展国内市场占有率，将国内市场立足于不败之地。同时，公司正试运行ISO22000食品安全管理体系，预计06年底通过食品安全管理体系审核。通过食品安全管理体系后，公司销售市场将向日本、韩国、马来西亚、新加坡、东南亚等国外市场进军；同时，以最短时间通过百胜、麦当劳、德克士公司审核，产品深加工，销售网络打入国内、国际快餐市场。 与临沂六和同期（05年）相比，我公司年销售量50000吨，是六和1.5倍；年销售收入总额高于六和0.4倍；微生物检验、理化检验、感官检验100%合格；产品出厂合格率100%，客户投诉为零；等数据67%都高于临沂六和。公司将不断持续严抓产品质量，极端突出公司产品优势。 总之，国内市场前景可观，国外市场一览宏图，公司以国内市场为基础，不断打造国际出口、国内国际快餐市场为目标的营销策略。不断质量改进，新品研发，产品会以安全、卫生及优质的服务赢得海内外消费者的青睐。
精心整理 二、填空题 1.PWM控制技术包括单极性控制和双极性控制两种方式。 2．反馈控制系统的作用是：抵抗扰动，服从给定。 3.静态环流可以分为直流平均环流和瞬时脉动环流。 4.PWM逆变器根据电源类型不同可以分为电压型和电流型。 5．直流电动机电枢的电流由负载决定。 20．V-M系统中，采用三相整流电路，为抑制电流脉动，可采用的主要措施是设置平波电抗器. 21．在单闭环调速系统中，为了限制全压启动和堵转电流过大，通常采用电流截止负反馈。22．在无静差的直流调速系统中，I部分的作用是__消除稳态误差____。 23．在α=β配合控制的直流可逆调速系统中，存在的是瞬时脉动环流，可用串接环流电抗器抑制。24．调速系统的稳态性能指标有调速范围、静差率。 25．某直流调速系统电动机的额定转速为n =1430r/min，额定速降为115r/min，要求静差率s≤30%， N 则系统允许的最大调速范围为。
26．转速、电流双闭环调速系统当中，两个调节器采用串联联接，其中转速反馈极性为负、电流反馈极性为负。 27．转速、电流双闭环系统，采用PI调节器，稳态运行时，转速n取决于给定电压、ASR的输出量取决于负载电流。 28．下图为单闭环转速控制系统。 (1)图中V是晶闸管整流器； 是平波电抗器，它的作用是抑制电流脉动和保证最小续流电流； (2)图中L d 37.在两组晶闸管反并联的可逆调速系统中，反转用正组晶闸管实现回馈制动的。 38、交流异步电动机调压调速工作时，其最大转矩随电机电压的降低而降低。 39、恒压频比控制方式是指给异步电动机供电的电压和之频率比为常数。 40、异步电动机变压变频调速控制特性曲线中，基频以下调速称为恒转矩调速，基频以上调速称为恒功率调速。 42、转速、电流双闭环直流调速系统中，对负载变化起抗扰作用的是转速调节器。 43、对于调速系统，最主要的抗扰性能是抗负载扰动和抗电网电压的性能。 44、在调速系统中常用的抗扰性能指标为动态降落和恢复时间。
一、填空题 1、直流电动机有三种调速方案：（1）调节电枢供电电压U；（2）减弱励磁磁通Φ；（3）改变电枢回路电阻R。 2、当电流大到一定程度时才出现的电流负反馈，叫做电流截止负反馈。 3、额定励磁状态下的直流电动机电枢电流与直流电动机的电磁转矩成正比。 4、他励直流电动机的调速方法中，调压调速是从基速（额定转速）往下调，在不同转速下容许的输出恒定，所以又称为恒转矩调速。调磁调速是从基速往上调，励磁电流变小，也称为弱磁调速，在不同转速时容许输出功率基本相同，称为恒功率调速。 5、直流调速系统的静态性能指标主要包括静差率和调速范围。 6、在比例积分调节调节过程中，比例部分的作用是迅速响应控制，积分部分的作用是消除稳态误差。 7、采用积分速度调节器的闭环调速系统是无静差的。 8、直流调速系统中常用的可控直流电源主要有旋转变流机组、静止式可控整流器和直流斩波器或脉宽调制变换器三种。 9、所谓稳态是指电动机的平均电磁转矩与负载转矩相平衡的状态。 10、在额定负载下，生产工艺要求电动机提供的最高转速和最低转速之比叫做调速范围。 11、负载由理想空载增加到额定值时所对应的转速降落与理想空载转速之比叫做静差率。 12、一个调速系统的调速范围，是指在最低转速时还能满足所需静差率的转速的可调范围。 13、反馈控制的作用是抵抗扰动、服从给定。 14、脉宽调制的方法是把恒定的直流电源电压调制成幅值相同、频率一定、宽度可变脉冲序列，从而可以改变平均输出电压的大小，以调节转速。 15、调速系统的要求有调速、稳速、加，减速。 16、直流电动机在调速过程中，若额定转速相同，则转速越低时，静差率越大。 17、在转速、电流双闭环直流调速系统中转速调节器的输出作为电流调节器的输入，再用电流调节器的输出去控制电力电子变换器。 18、双闭环调速系统在正常运行时， ACR 调节器是不会达到饱和的。 19、反馈控制系统所能抑制的知识被反馈环包围的前向通道上的扰动。 20、一般来说，调速系统的的动态指标以抗扰性能为主，而随动系统的动态性能指标则以跟随性能为主。 21、转速、电流双闭环直流调速系统在起动过程中，转速调节器ASR经历了不饱和、饱和、退饱和三种情况。 22、双闭环调速系统的起动过程分为三个阶段，即电流上升阶段、恒流升速介段、转速调节阶段。 23、双闭环系统由于起动过程中转速调节器饱和，使电动机一直处于最大起动电流。 24、转速、电流双闭环系统在恒流升速阶段转速调节器饱和，电流调节器不饱和。 25、在转速、电流双闭环系统中，出现电网波动时，电流调节器其主要作用；出现负载扰动时，转速调节器其主要作用。 26、在双闭环系统中中引入转速微分负反馈抑制转速超调，显著地降低（填增加或减少）动态速降，提高抗扰性能。27、V-M系统的可逆线路有两种方法，即电枢反接可逆线路和励磁反接可逆线路。 28、变流装置有整流和逆变两种状态，直流电动机有电动和制动两种状态。 29、逻辑无环流可逆调速系统的结构特点是在可逆系统增加DLC，称为无环流逻辑控制环节，包括电平检测、逻辑判断、延时电路、联锁保护四部分，它的功能是根据系统运行情况实时地封锁原工作的一组晶闸管脉冲，然后开放原封锁的一组晶闸管的脉冲。 30、环流是指不流过电动机或其他负载，而直接在两组晶闸管之间流通的短路电流。 31、无环流可逆调速系统可按实现无环流的原理的不同分为逻辑无环流系统和和错位控制无环流系统。 32、有环流可逆调速系统中采用 β ≥ ?配合控制时可消除直流平均环流；设置环流电抗器可抑制瞬时脉动换流。 33、在转速、电流双闭环调速系统中，转速调节器按典型 II 型系统设计，其抗干扰能力 好，稳态无误差；电流调节器按典型 I 型系统设计，其抗干扰能力差，超调较小。 34、异步电动机变压变频调速系统必须具备能同时控制电压幅值和频率的交流电源。 35、电压型变频器的主电路包括整流电路、中间直流电路、逆变电路三部分。 36、根据直流环节的储能方式分，交-直-交变频器可分为电压型和电流型。 37、对异步电动机进行调速控制时，希望电动机的主磁通保持额定值不变。磁通太弱，铁心利用不充分；磁通太强，则铁心饱和，导致励磁电流过大。 38、异步电动机变频调速是靠改变电动机供电频率调速，而其转差频率控制方式中控制的是转差角频率，故可将电动机转差角频率与电动机转速信号相加获得定子给定频率，就可对定子频率进行控制。 39、异步电动机调速，按对转差功率处理方式的不同，交流调速系统可分为转差功率消耗型调速系统、 转差功率回馈型调速系统、转差功率不变型调速系统三类。 40、变频器的转差频率控制方式的控制思想是建立在异步电动机的稳态数学模型的基础上。 41、按照异步电动机的工作原理，电磁功率和机械功率的关系为 mech P= 1-s m P，电磁功率和转差功率的关系为 Ps=sPm 。 42、异步电动机变压调速系统，当电压减小时，最大电磁转矩减小，最大电磁转矩所对应的转差率减小。（减小、增大、不变） 43、SPWM的调制方式有同步调制、异步调制、分段同步调制和混合调制。 44、SPWM逆变器是利用正弦波信号与三角波信号相比较后，而获得一系列等幅不等宽的脉冲波形。 45、矢量控制系统的基本思想是通过坐标变换得到等效的两相数学模型，然后按转子磁链定向，将交流电动机定子电流分解为励磁分量和转矩分量，从而可以获得和直流电动机相仿的高动态性能。 46、异步电动机三相动态模型结构复杂，采用坐标变换和矩阵变换可简化动态数学模型，坐标变换的原则是磁动势不变。 47、同步电动机的转子旋转速度就是同步转速，转差 S ω恒等于 0 。 48、同步电动机的变压变频调速系统属于转差功率不变型的调速系统。 1
《运动控制系统》课程设计报告 时间2014.10 _ 学院自动化 _ 专业班级自1103 _ 姓名曹俊博__ 学号 指导教师潘月斗 ___ 成绩 _______
摘要 本课程设计从直流电动机原理入手，建立V-M双闭环直流调速系统，设计双闭环直流调速系统的ACR和ASR结构，其中主回路采用晶闸管三相桥式全控整流电路供电，触发器采用KJ004触发电路，系统无静差；符合电流超调量σi≤5%；空载启动到额定转速超调量σn≤10%。并详细分析系统各部分原理及其静态和动态性能，且利用Simulink对系统进行各种参数给定下的仿真。 关键词：双闭环；直流调速；无静差；仿真 Abstract This course is designed from DC motor, establish the principles of V-M double closed loop DC speed control system design, the double closed loop dc speed control system and the structure, including ACR ASR the main loop thyristor three-phase bridge type all control the power supply and trigger the rectifier circuit KJ004 trigger circuit, the system without the static poor; Accord with current overshoots sigma I 5% or less; No-load start to the rated speed overshoot sigma n 10% or less. And detailed analysis of the system principle and the static and dynamic performance, and the system of simulink to various parameters set simulation. Key Words：double closed loop；DC speed control system；without the static poor；simulation
2020年【科技】行业市场调研及前景预测分析报告 2020年2月
目录 1. 科技行业概况及市场分析 (6) 1.1 科技行业发展现状分析 (6) 1.2 科技行业结构分析 (6) 1.3 科技行业市场规模分析 (6) 1.4 科技行业PEST分析 (7) 1.5 科技行业市场运行状况分析 (9) 1.6 科技行业特征分析 (11) 2. 科技行业驱动 (11) 2.1 市场驱动分析 (11) 2.2 人口红利将会持续利好行业发展 (13) 2.3 一级市场火热，国内专利不断攀升 (13) 2.4 宏观环境下科技行业的定位 (14) 2.5 “十三五”期间科技建设取得显著业绩 (14) 3. 科技产业发展前景 (15) 3.1 中国科技行业市场规模前景预测 (15) 3.2 科技进入大面积推广应用阶段 (16) 3.3 中国科技行业市场增长点 (17) 3.4 细分化产品将会最具优势 (18) 3.5 科技产业与互联网等产业融合发展机遇 (18) 3.6 科技人才培养市场大、国际合作前景广阔 (19) 3.7 巨头合纵连横，行业集中趋势将更加显著 (20)
3.8 建设上升空间较大，需不断注入活力 (20) 3.9 行业发展需突破创新瓶颈 (21) 4. 科技行业竞争分析 (22) 4.1 科技行业国内外对比分析 (22) 4.2 中国科技行业品牌竞争格局分析 (24) 4.3 中国科技行业竞争强度分析 (24) 4.4 初创公司大独角兽领衔 (25) 4.5 上市公司双雄深耕多年 (26) 4.6 互联网巨头综合优势明显 (26) 5. 科技行业存在的问题分析 (28) 5.1 基础工作薄弱 (28) 5.2 地方认识不足，激励作用有限 (28) 5.3 产业结构调整进展缓慢 (28) 5.4 技术相对落后 (28) 5.5 隐私安全问题 (29) 5.6 与用户的互动需不断增强 (29) 5.7 管理效率低 (30) 5.8 盈利点单一 (31) 5.9 过于依赖政府，缺乏主观能动性 (31) 5.10 法律风险 (31) 5.11 供给不足，产业化程度较低 (32) 5.12 人才问题 (32)
市场前景分析怎么写 篇一：项目可行性分析报告经典范文 项目可行性分析报告 一、企业基本情况： 1..企业名称：江西省富豪实业有限公司富皇五金加工厂 2.经济性质：有限责任公司 3.注册地址：江西省萍乡市 4.通讯地址：江西省萍乡市康庄路31号 5经营期限：长期 6.注册资金：万 投资估算： 二、项目背景 （一）可行性报告编制依据 1. 国家政策的支持和地方政府的发展目标相统一。 中国扩大内需政策成为行业发展长期内生动力，目前我国已经进入经济结构调整阶段，作为3架马车的消费作用越来越明显，通过扩大内需来拉动经济增长已经成为必然趋势。“十二五”规划中提出要建立扩大消费需求的长效机制，把扩大消费作为扩大内需的战略重点，未来几年将增增加居民消费能力，释放成乡居民消费潜力。 我国皮包五金配件行业已经具备了较为完备的基础条件，良好的社会经济环境，广阔的市场空间，完善的工业配套体系，国家历来重视该领域的发展，相关引导和鼓励性政策频频发布，为行业发展注入政策动力。 我国五金行业经过十几年的积累和稳步提高，现在已是世界上产量最大的国家。现在国内金属制品工业销售收益逐年增长，增长率坚持在14% 以上，市场规模不时扩大。2006 年该行业销售 收益到达8123.52 亿元，增长率达29.39%, 近七年。比拟2000 年市场规模扩大了2.62 倍。海内经济与工业突飞大进之下，大量五金零件需求旺盛，市场规模扩大。国金属制品行业产销率均保持在工业标准值96% 以上，近七年。市场产销配比合理。从2011年9月，国务院召开促进中小企业发展领导小组会议，进一步研究扶持中小企业发展的政策措施，同时，根据三中全会的精神和政策，支持和引导皮包五金配件的生产和加工。 2.当地广阔的市场空间的需要。 目前就萍乡市的小五金企业的市场状况来看，目前萍乡市都没有一个相对大型的生产小五金的企业，萍乡市的小五金大多都是从外地采购过来。对此，就目前看来，在当地建立一个小五金的加工生产基地，很大程度能够解决当地市场的需求，并且能够最大程度的节省需求者的成本。因此，直接在当地建立一个小五金的生产企业，解决当地市场的供需。 （二）必要性和可行性 1.必要性 对于小五金的生产来说，在萍乡市建立一个统一的小五金加工生产时非常有必要的。现在我们面对的主要是整个萍乡市的生产皮包的企业，为其提供挂牌，拉环等一系列的小五
《运动控制系统》课程教学大纲 大纲执笔人：大纲审核人： 课程编号：0808000555 英文名称：Motion control system 学分：4 总学时：64。其中，讲授54 学时，实验 10 学时，上机 0 学时，实训 0 学时。 适用专业: 自动化 先修课程：自动控制原理、现代控制理论基础、电力电子技术 一、课程性质与教学目的 《运动控制系统》是一门讲授交、直流电动机控制理论和控制规律，以提高电能利用效率及运动控制品质的一门专业主干课程，是自动化专业的一门必修课。其目的是使学生了解并掌握各类交、直流电动机控制系统的基本结构、工作原理和性能指标，着重培养学生对运动控制系统的综合分析能力和工程设计能力，从而掌握现代交、直流电动机的控制理论和系统设计方法，为今后从事专业工作打下扎实的基础。 二、基本要求 本课程秉承理论与实际相结合的理念，应用自动控制理论解决运动控制系统的分析和设计问题，以转矩和磁链（或磁通）控制规律为主线，由简入繁、由低及高地循序深入，论述系统的静、动态性能。通过本课程的学习，要求学生能够了解运动控制系统的定义、结构及其分类，理解运动控制的必要性，掌握单、双闭环直流电动机调速系统、VVVF变频器、交流异步电动机矢量控制系统、正弦波永磁同步电动机调速系统、位置控制系统等的结构与原理、分析与设计方法。 三、重点与难点 1. 课程重点 （1）直流调速系统：以直流电动机为对象组成的运动控制系统，转速单闭环调速系统，转速、电流双闭环控制调速系统的基本组成和控制规律，静态、动态性能分析，直流调速系统的工程设计方法，直流调速系统的数字控制方法。 （2）交流调速系统：异步电动机的稳态模型及基于稳态模型的交流调速系统，异步电动机的动态模型及基于动态模型的高性能交流调速系统，同步电动机变频调速系统。 2、课程难点 （1）双闭环直流调速系统：通过双闭环直流调速系统静、动态模型研究及性能分析，对转速与电流环的典型系统校正，推导PI 控制规律与工程计算方法。 （2）空间电压矢量PWM：从稳态和动态、时域和空间等方面论述矢量、标量、相量的区别与联系，各自的表现形式，基本特征与物理意义。 （3）异步电动机动态数学模型：依据旋转磁场产生原理，论述时间和空间变量的相对关系，讨论静止与旋转（或交变）的关系与转化，理解在各种坐标系下的数学模型。通过计算机数字仿真，分析比较各种物理量在不同坐标系的表现形式和相互间的联系。 （4）矢量控制系统：着重论述按转子磁链定向，定子电流转矩分量和励磁分量的解耦，等效
运动控制直流部分复习题 一、填空： 1. 调速系统的稳态性能指标主要是指和静差率。 2. 采用V-M系统，当系统处于深调速状态时，功率因数将较。 3. 直流调速系统中，晶闸管触发和整流装置的传递函数可近似成环节， 时间常数称为。 4. 晶闸管-电动机转速、电流双闭环调速系统中，环为内环，环为 外环。 5. 双惯性环节校正成典型Ⅰ型系统，引入的调节器是调节器。 6 直流调速的方法包括改变电枢回路电阻调速、调速和减弱磁通调速。7．闭环调速系统对于_ 的扰动具有抑制作用，而对于_ _的扰动则无能为力。 8．转速、电流双闭环调速系统中，调节_ _的限幅值可以调节系统最大电流；调节_ _的限幅值可以调节UPE的最大输出电压。 9．双极性直流PWM变换器的占空比，当时，输出平均电压为正，要使输出平均电压为负，应使。 二、选择题 1.下列说法正确的是（） A 积分调节器的输出决定于输入偏差量的历史过程。 B 比例控制可以使系统在偏差电压为零时保持恒速运行。 C 比例调节器可以实现无静差。 D 采用积分调节器动态相应快。 2.双闭环调速系统中电流调节器具备的作用为（） A 对负载变化起抗扰作用。 B 对电网电压波动起及时抗扰作用。 C 输出限幅决定允许的最大电流。 D 使转速跟随转速给定电压变化。 3.双闭环调速系统中转速调节器不具备的作用为（） A 对负载变化起抗扰作用。 B 对电网电压波动起及时抗扰作用。 C 输出限幅决定允许的最大电流。 D 使转速跟随给定电压变化。 4.在工程设计中，如果将系统校正成典型Ⅰ型系统的过程，KT值取为（）时为无超调。
A B C D 5. 采用工程设计法的双闭环直流调速系统中，电流环设计成典型（）型系统，引入的电流调节器为（）调节器。 A ⅠPI B ⅡPI C ⅠP D ⅡP 6. G-M直流调速系统中的G指的是哪一种直流电源（）。 A 直流发电机； B 静止整流器； C 脉宽调制电源； D 以上情况均可能。 三、分析与简答 1.在调速系统中，为什么在开环系统中晶闸管整流装置的控制电压前面没有加放大器，而在闭环之后要添加放大器？ 2. 双闭环调速系统中，电流调节器的作用各是什么？ 3.采用双极型PWM变换器的调速系统，当电动机停止时，电枢电流是否等于零，为什么？ 4. 假设某转速单闭环调速系统的电源电压突然降低，则该调速系统将如何进行 调节，请结合稳态结构图加以说明。 5. 转速、电流双闭环直流调速系统设计后，ASR限幅对应倍额定电流，但是在空 载额定励磁稳速运行时突加额定转矩负载，转速不能回到给定转速，请分析原因？ 6. 在转速、电流双闭环直流调速系统中，两个调节器均采用PI调节器。当系统带 额定负载运行时，转速反馈线突然断线，试分析系统进入稳态后调节器、转速、电枢电流的情况。 7. 写出直流电动机反馈闭环调速系统的临界放大系数表达式，并请说明表达式中各个参数含义。 8. 请写出双闭环调速系统起动过程的三个特点。 9. 请简述H型双极式PWM变换器的缺点。 四、设计题 1、某晶闸管供电的双闭环直流调速系统，整流装置采用三相桥式电路，基本数据如下： 直流电动机220V、136A、1460r/min，C e=r，允许过载倍数λ=。 晶闸管装置放大系数40。 电枢回路总电阻Ω。 时间常数T l=，T m=。 电流反馈系数β=A（≈10V/），转速反馈系数α=r（≈10V/n N）。 将电流环校正成典型Ⅰ型系统，取KT=；将转速环校正成典型Ⅱ型系统，取h=5。电流环滤波时间常数；转速环滤波时间常数。 请选择并设计各调节器参数。 2、有一转速、电流双闭环调速系统,已知电动机参数为：P N =，U N =220V， I N=28A，n N=1490 r/min，电枢回路电阻R=Ω,允许电流过载倍数λ=，电 磁时间常数T L=，机电时间常数T m=，主电路采用三相桥式整流电路，触 发整流环节的放大倍数Ks=35，整流电装置内阻R res=Ω，平均失控时间常
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目录 小米行业市场前景预测及机会分析 (3) 第一节行业市场前景预测 (3) 一、市场供需预测 (3) 二、生产规模预测 (3) 三、市场需求预测 (5) （一）全国 (5) （二）华北地区 (6) （三）山东省 (6) （四）北京市 (7) 第二节发展趋势预测 (7) 一、培养高产品种 (7) 二、加强谷子的营养研究，研发大众化食品，促进谷子生产的产业 化和规模化 (9) 三、树立谷子产业思想，全面规划和研究谷子产业发展 (10) 第二节细分市场机会分析 (11) 1、小米饮品（包含酒品） (11) 2、小米糕点（包含饼干） (11) 3、即食小米粥 (12) 第三节新进入者投资机会分析 (13) 2
3 小米行业市场前景预测及机会分析 第一节 行业市场前景预测 一、市场供需预测 小米已经从北方人独好变为全国人热捧，由相关营养组织建议，人均杂粮摄入量应在50g-100g ，以人均年消费小米1kg 计，我国每年小米需求量将达到140万吨。 而随着人们对健康的日益关注，未来几年我国小米的供给量和需求量都将不断上升，保持供不应求的状态，与此同时二者之间的供需缺口会进一步扩大。 根据2009-2014 年我国小米供需发展情况对2015-2019年我国小米行业发展进行如下预测： 图表- 1：2015-2019年我国小米供需预测 中企智业整理 二、生产规模预测 从育种目标方面分析，1995年以前，我国谷子育种目标基本上以高产为主，产量水平明显提高，育成了以豫谷1号、昭谷1号、冀谷14号等为代表的高产多抗品种。1996年以来，优质育种取得突破性进展，实现了高产、优质的统一，育成了以冀谷17号、小香米、豫谷9号、晋谷34号、晋谷35号、晋谷36号、
1 运动控制系统的任务是通过对电动机电压、电流、频率等输入电量的控制，来改变工作机械的转矩、速度、位移等机械量，使各种工作机械按人们期望的要求运行，以满足生产工艺及其他应用的需要。（运动控制系统框图） 2. 运动控制系统的控制对象为电动机，运动控制的目的是控制电动机的转速和转角，要控制转速和转角，唯一的途径就是控制电动机的电磁转矩，使转速变化率按人们期望的规律变化。因此，转矩控制是运动控制的根本问题。 第1章可控直流电源-电动机系统内容提要 相控整流器-电动机调速系统 直流PWM变换器-电动机系统 调速系统性能指标 1相控整流器-电动机调速系统原理 2.晶闸管可控整流器的特点 （1）晶闸管可控整流器的功率放大倍数在104以上，其门极电流可以直接用电子控制。（2）晶闸管的控制作用是毫秒级的，系统的动态性能得到了很大的改善。 晶闸管可控整流器的不足之处 晶闸管是单向导电的，给电机的可逆运行带来困难。 晶闸管对过电压、过电流和过高的du/dt与di/dt都十分敏感，超过允许值时会损坏晶闸管。 在交流侧会产生较大的谐波电流，引起电网电压的畸变。需要在电网中增设无功补偿装置和谐波滤波装置。 3.V-M系统机械特 4.最大失控时间是两个相邻自然换相点之间的时间，它与交流电源频率和晶闸管整流器的类型有关。 5.（1）直流脉宽变换器根据PWM变换器主电路的形式可分为可逆和不可逆两大类 （2）简单的不可逆PWM变换器-直流电动机系统 （3）有制动电流通路的不可 逆PWM-直流电动机系统 （4）桥式可逆PWM变换器 （5）双极式控制的桥式可逆PWM变换器的优点 双极式控制方式的不足之处 （6）直流PWM变换器-电动机系统的能量回馈问题 ”。（7）直流PWM调速系统的机械特性 6..生产机械要求电动机在额定负载情况下所需的最高转速和最低转速之比称为调速范围，用字母D来表示（D的表达式） 当系统在某一转速下运行时，负载由理想空载增加到额定值时电动机转速的变化率，称为静差率s。 D与s的相互约束关系 对系统的调速精度要求越高，即要求s越小，则可达到的D必定越小。 当要求的D越大时，则所能达到的调速精度就越低，即s越大，所以这是一对矛盾的指标。第二章闭环控制的直流调速系统 内容提要 ?转速单闭环直流调速系统 ?转速、电流双闭环直流调速系统 调节器的设计方法 1.异步电动机从定子传入转子的电磁功率可分成两部分：一部分是机械轴上输出的机械功率；另一部分是与转差率成正比的转差功率。.异步电动机按调速性能分类第一类基于稳态模型，动
2020年【黄金】行业市场调研及前景预测分析报告 2020年3月
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