*仅供参考
上海电力学院
毕业设计（英文翻译）
课题名称认知无线电频谱感知算法仿真
院（系）
专业
班级
学生
学号
Implementation Issues in Spectrum Sensing for Cognitive Radios
认知无线电频谱感知的实现问题
Abstract:There are new system implementation challenges involved in the design of cognitive radios, which have both the ability to sense the spectral environment and the flexibility to adapt transmission parameters to maximize system capacity while co-existing with legacy wireless networks. The critical design problem is the need to process multi-gigahertz wide bandwidth and reliably detect presence of primary users. This places severe requirements on sensitivity, linearity, and dynamic range of the circuitry in the RF front-end. To improve radio sensitivity of the sensing function through processing gain we investigated three digital signal processing techniques: matched filtering, energy detection, and cyclostationary feature detection. Our analysis shows that cyclostationary feature detection has advantages due to its ability to differentiate modulated signals, interference and noise in low signal to noise ratios. In addition, to further improve the sensing reliability, the advantage of a MAC protocol that exploits cooperation among many cognitive users is investigated.
摘要：出现了一些新系统的实施挑战，其涉及认知无线电——具有感知频谱环境下的传输参数既适应能力和灵活性，以最大限度地提高系统容量，同时并存于传统无线网络。关键设计问题是需要处理多千兆赫宽的带宽，可靠地检测主用户的存在。这对灵敏度，线性度和在RF前端电路的动态范围有严格要求。为了通过处理增益而提高无线电灵敏度，我们调查了三种数字信号处理技术的感测功能：匹配滤波，能量检测和循环平稳特征检测。我们的分析表明：由于能够区分调制信号，干扰和噪声在低信噪比，循环平稳特征检测更有优势。此外，为了进一步提高检测的可靠性，MAC协议，它利用在许多认知用户合作的优势已经在这一块研究很久了。
I. INTRODUCTION
一、介绍
1.
It is commonly believed that there is a spectrum scarcity at frequencies that can be economically used for wireless communications. This concern has arisen from the intense competition for use of spectra at frequencies below 3 GHz. The Federal Communications Commission’s (FCC) frequency allocation chart indicates overlapping allocations over all of the frequency bands, which reinforces the scarcity mindset. On the other hand, actual measurements taken in downtown Berkeley are believed to be typical and indicate low utilization, especially in the 3-6 MHz bands. Figure 1 shows the power spectral density (PSD) of the received 6 GHz wide
signal collected for a span of 50μs sampled at 20 GS/s [12]. This view is supported by recent studies of the FCC’s Spectrum Policy Task Force who reported [1] vast temporal and geographic variations in the usage of allocated spectrum with utilization ranging from 15% to 85%. In order to utilize these spectrum ‘white spaces’, the FCC has issued a Notice of Proposed Rule Making (NPRM –FCC 03-322 [2]) advancing Cognitive Radio (CR) technology as a candidate to implement negotiated or opportunistic spectrum sharing.
人们普遍认为，有一个频谱稀缺的频率，可以经济地用于无线通信。从使用3 GHz以下频率光谱的激烈竞争开始，它就越来越受到关注。美国联邦通信委员会（FCC）的频率分配图表显示所有频段都有重叠的分配，这加强了稀缺的现状。另一方面，在伯克利市中心采取的实际测量被认为是典型的实验结果，从中指出频谱利用率低，特别是在3-6 MHz频段。图1
显示接收到的6千兆赫的功率谱密度（PSD）宽信号，50μs的采样在20 GS / s的的一个跨度。这种观点是最近FCC的频谱政策任务组的研究报告，报告称浩瀚时空和地域变化在分配的频谱利用率介乎15％至85％的使用。为了利用这些频谱'空白'，FCC已发出建议规则制定的通知（NPRM - FCC03-322[2]）推进认知无线电（CR）技术，以实现协商或伺机频谱共享的候选人。
2.
Wireless systems today are characterized by wasteful static spectrum allocations, fixed radio functions, and limited network coordination. Some systems in unlicensed frequency bands have achieved great spectrum efficiency, but are faced with increasing interference that limits network capacity and scalability. Cognitive radio systems offer the opportunity to use dynamic spectrum management techniques to help prevent interference, adapt to immediate local spectrum availability by creating time and location dependent in “virtual unlicensed bands”, i.e. bands that are shared with primary users. Unique to cognitive radio operation is the requirement that the radio is able to sense the environment over huge swaths of spectrum and adapt to it since the radio does not have primary rights to any pre-assigned frequencies. This new radio functionality will involve the design of various analog, digital, and network processing techniques in order to meet challenging radio sensitivity requirements and wideband frequency agility.
现在无线系统的特点是浪费的静态频谱分配，固定无线功能，以及有限的网络协调。在未经许可的频带一些系统已经取得了很大的频谱效率，但都面临着限制的网络容量和可扩展性增加的干扰。认知无线电系统提供使用动态频谱管理技术，以帮助防止干扰，通过创建时间和位置相关的“虚拟免授权频段”，适应当地的即时频谱可用性的机会，例如与主要用户共享频段。独特的认知无线电操作是有需要的，它使无线电能够通过频谱巨大的大片感知环境，并适应它，纵然无线电对任何预指配频率没有基本权利。这种新的无线功能将涉及各种模拟设计，数字化和网络处理技术，以满足具有挑战性的射频灵敏度的要求和宽带频率捷变。
3.
Spectrum sensing is best addressed as a cross-layer design problem. Cognitive radio sensitivity can be improved by enhancing radio RF front-end sensitivity, exploiting digital signal processing gain for specific primary user signal, and network cooperation where users share their spectrum sensing measurements.
频谱感知在跨层设计问题上是最好的方法。认知无线电的灵敏度可以通过增强无线电射频前端的灵敏度，利用数字信号处理增益为特定主用户信号，以及网络合作，用户共享他们的频谱感测的测量得到改善。
4.
The paper is organized as follows; Section II defines spectrum sensing function and proposes a cross-layer approach for its implementation. Section III considers RF front-end and A/D requirements for spectrum sensing and analog techniques for feasible implementations. In section IV we investigate digital signal processing techniques that can improve radio sensitivity and detect primary users’presence. Section V presents the results from a cooperative sensing scheme, achievable gains and implementation issues. Finally, conclusions are presented in Section VI.
本文结构如下，第二部分定义频谱感知功能，并提出了实施一个跨层的方法。第三部分讨论频谱感知的射频前端，后端和A / D的要求，与可实现的模拟技术。在第四部分中，我们研究，可以提高无线电灵敏度和检测主用户的存在的数字信号处理技术。第五部分提出了从协作感知方案，可实现收益和实施问题的结果。最后，结论载于第六部分。
II. SPECTRUM SENSING
二、频谱感知
1.
A “Cognitive Radio”is a radio that is able to sense the spectral environment over a wide frequency band and exploit this information to opportunistically provide wireless links that best meet the user communications requirements [2]. While many other characteristics have also been discussed as possible additional capabilities, we will use this more restricted definition and consider physical (PHY) and medium access control (MAC) functions that are linked to spectrum sensing as illustrated in Figure 2
认知无线电是一种无线电，它能够感觉到在很宽的频带内的频谱环境，并利用这些信息来投机提供最能满足用户的通信需求的无线链路。在许多其他特性也已讨论过作为可能的附加功能时，我们将使用这个更受限制的定义，并考虑物理层（PHY）和介质访问控制（MAC）功能链接到频谱感测，如图2
2.
Since cognitive radios are considered lower priority or secondary users of spectrum allocated to a primary user, a fundamental requirement is to avoid interference to potential primary users in their vicinity. On the other hand, primary user networks have no requirement to change their infrastructure for spectrum sharing with cognitive networks. Therefore, cognitive radios should be able to independently detect primary user presence through continuous spectrum sensing. For example, TV broadcast signals are much easer to detect than GPS signals, since the TV receivers’sensitivity is tens of dBs worse than GPS receiver.
由于认知无线电被认为是低优先级或分配给主用户频谱的二级用户，一个基本要求是，避免附近的有潜力的主要用户的干扰。另一方面，主用户网络具有不要求改变他们与认知网络频谱共享的基础设施。因此，认知无线电应该能够通过不断的频谱感知独立检测主用户的存在。例如，广播电视信号更容易比GPS信号来检测，因为电视接收器的灵敏度是几十分贝比GPS 接收器差。
3.
In general, cognitive radio sensitivity should outperform primary user receiver by a large margin in order to prevent what is essentially a hidden terminal problem. This is the key issue that makes spectrum sensing very challenging research problem. Meeting the sensitivity requirement of each primary receiver with a wideband radio would be difficult enough, but the problem becomes even more challenging if the sensitivity requirement is raised by additional 30-40 dB. This margin is required because cognitive radio does not have a direct measurement of a channel between primary user receiver and transmitter and must base its decision on its local channel measurement to a primary user transmitter. This type of detection is referred to as local spectrum sensing and the worst case hidden terminal problem would occur when the cognitive radio is shadowed, in severe multipath fading, or inside buildings with high penetration loss while in a close neighborhood there is a primary user whose is at the marginal reception, due to its more favorable channel conditions. Even though the probability of this scenario is low, cognitive radio should not cause interference to such primary user.
一般情况下，认知无线电灵敏度应远远胜过主用户接收器，为的是防止出现隐藏终端问题。这是使频谱感知非常具有挑战性的研究课题的关键问题。满足每个主接收器的灵敏度要求，宽带无线电将难以足够了，但如果灵敏度的要求是提出额外的30-40分贝的问题就变得更加具有挑战性。这个利润率是必需的，因为认知无线电没有直接测量主用户接收机和发射机之间的信道，并且必须立足其上的本地信道测量决定主要用户发送。这种类型的检测被称为本地频谱检测和当认知无线电是阴影，在严重的多径衰落会发生隐藏终端问题的最坏的情况下，在严重的多径衰落，或内部具有高穿透损耗的物体，而在一个近邻域有一个主要用户，其是在边缘接收，由于其更有利的信道条件。即使这种情况的概率较低，认知无线电应该不会对这样的主用户造成干扰。
4.
The implementation of the spectrum sensing function also requires a high degree of flexibility since the radio environment is highly variable, both because of different types of primary user systems, propagation losses, and interference. The main design challenge is to define RF and analog architecture with right trade-offs between linearity, sampling rate, accuracy and power, so that digital signal processing techniques can be utilized for spectrum sensing, cognition, and
adaptation. This also motivates research of signal processing techniques that can relax challenging requirements for analog, specifically wideband amplification, mixing and A/D conversion of over a GHz or more of bandwidth, and enhance overall radio sensitivity.
频谱检测功能的实现也需要高度灵活性，由于无线环境是高度可变，另一个原因是不同类型的主用户系统中存在传播损耗和干扰。主要的设计挑战是定义射频和模拟结构与线性，采样率，精度和功率之间权利权衡，以使数字信号处理技术可被用于频谱感知，认知和适应。这也促使了可以放宽对模拟的，特别宽频带放大，混合和超过带宽的GHz或多个A/ D转换的挑战性的要求，提高整体的无线电灵敏度的信号处理技术的研究。
III. COGNITIVE RADIO FRONTEND
三、认知无线电前端
1.
There are two frequency bands where the cognitive radios might operate in a near future: 400-800 MHz (UHF TV bands) and 3-10 GHz. The FCC has noted that in the lower UHF bands almost every geographical area has several unused 6 MHz wide TV channels. This frequency band is particularly appealing due to good propagation properties for long-range communications. Furthermore, given the static TV channel allocations, the timing requirements for spectrum sensing are very relaxed. The FCC approval of UWB underlay networks in 3-10 GHz indicates that this frequency range might be opened for opportunistic use. Furthermore, this band has very low spectral utilization, as indicated in Figure 1.
有两个频带，其中的认知无线电设备可能在不久的将来操作：400-800MHz的（UHF电视频段）和3-10千兆赫。美国联邦通信委员会已经注意到，在较低的UHF频段几乎每一个地区有几个未使用的6 MHz宽的电视频道。该频段是由于远距离通信良好的传播特性特别有吸引力。此外，鉴于静态电视频道的分配，对时序要求频谱感知是很轻松的。FCC认证表明在3-10 GHz的超宽带底层网络，该频率范围内可能会开始使用。此外，该带具有非常低的频谱利用，如图1所示。
2.
Regardless of operating frequency range, a wideband front-end for a cognitive radio could have an architecture as depicted in Figure 3. The wideband RF signal presented at the antenna of a cognitive radio includes signals from close and widely separated transmitters and from transmitters operating at widely different power levels and channel bandwidths. As a result, detection of weak signals must frequently be performed in the presence of very strong signals. Thus, there will be extremely stringent requirements placed on the linearity of the RF analog circuits as well as their ability to operate over wide bandwidths. In order to keep the requirements on the final analog to digital (A/D) converter at a reasonable level in a mostly digital architecture, front-end design needs a tunable notch analog processing block that would provide a dynamic range control.
不论工作频率范围，宽带前端的认知无线电可以有一个体系结构，如图3所示。在认知无线电的天线提出的宽带射频信号包括从密切和广泛分离发射器和在广泛的不同功率级别和信道带宽操作发射器的信号。其结果，必须频繁地在非常强的信号的存在下进行检测微弱信号。因此，将对RF模拟电路的线性度，以及电路工作在宽的带宽的能力提出极为严格的要求。为了保持对最终模拟的要求，它需要模数（A/ D）转换器处在一个多数字结构合理水平，所
以前端设计需要一个可调陷波模拟处理模块以提供动态范围控制。
3.
Reducing the in-band interference to a manageable level is a critical design problem, since the traditional strategy of narrow band analog frequency selective filtering to avoid the wide dynamic range of interfering signals is not viable. The ultimate solution to this problem would involve a combination of techniques, including adaptive notch filtering such as employed in UWB designs, banks of on chip RF filters possibly using MEMS technology such as FBAR’s, and spatial filtering using RF beam-forming through adaptive antenna arrays. Other more sophisticated approaches could involve active cancellation, because in the situation in which the interfering signal is extremely strong, it is then possible to decode the signal and provide an active canceling signal before the A/D conversion process. While the active cancellation approach will consume significantly more hardware, it has the important advantage of ultimately being more flexible.
减少了带内干扰到一个可管理的水平是一个关键的设计问题，因为窄带模拟频率选择性滤波的传统策略，以避免干扰信号是不可行的宽动态范围。最终解决这一问题将涉及的技术的组合，包括自适应陷波滤波器，如在超宽带设计采用，对芯片射频银行滤波器可能使用MEMS 技术，如FBAR的，并使用通过自适应天线阵列射频波束形成空间滤波。其它更复杂的方法可涉及有源取消，因为在干扰信号是非常强的情况下，那么有可能对信号进行解码，并在A / D转换处理前提供一个有源抵消信号。而活性消除方法会消耗显著更多的硬件，它具有最终处理更灵活的重要优势。
4.
The spatial dimension provides several new opportunities. The sensitivity of the sensing receiver can be increased by the exploitation of multiple antennas through diversity increase and range extension, which in effect could make it much more sensitive than the primary users which it is trying to detect.
空间维度提供了一些新的机遇。传感接收器的灵敏度的增强可以通过减少多个天线来实现，这是因为多样性的增加和范围扩大，这实际上可能使比它试图检测主用户来说更加敏感。
IV. SIGNAL PROCESSING TECHNIQUES FOR SPECTRUM SENSING
四、频谱感知的信号处理技术
1.
A key advantage of CMOS integration is that digital signal processing can be used to assist the analog circuits. In case of spectrum sensing the need for signal processing is two-fold: improvement of radio front-end sensitivity by processing gain and primary user identification
based on knowledge of the signal characteristics. In this section we discuss advantages and disadvantages of three techniques that are used in traditional systems: matched filter, energy detector and cyclostationary feature detector.
CMOS集成的一个主要优点是，数字信号处理可以用来协助模拟电路。在频谱感知需要的信号处理是双重的情况下：通过处理增益和主用户基于信号特征知识的识别，无线电前端灵敏度有所进步。在本节中，我们讨论用于传统系统的三种技术的优点和缺点：匹配滤波器，能量检测和循环平稳特征检测器。
2.
A. Matched Filter
The optimal way for any signal detection is a matched filter,since it maximizes received signal-to-noise ratio. However, a matched filter effectively requires demodulation of a primary user signal. This means that cognitive radio has apriori knowledge of primary user signal at both PHY and MAC layers, e.g. modulation type and order, pulse shaping, packet format. Such information might be pre-stored in CR memory, but the cumbersome part is that for demodulation it has to achieve coherency with primary user signal by performing timing and carrier synchronization, even channel equalization. This is still possible since most primary users have pilots, preambles, synchronization words or spreading codes that can be used for coherent detection. For examples: TV signal has narrowband pilot for audio and video carriers; CDMA systems have dedicated spreading codes for pilot and synchronization channels; OFDM packets have preambles for packet acquisition. The main advantage of matched filter is that due to coherency it requires less time to achieve high processing gain since only O(1/SNR) samples are needed to meet a given probability of detection constraint. However, a significant drawback of a matched filter is that a cognitive radio would need a dedicated receiver for every primary user class.
A.匹配滤波器
对于任何信号检测的最佳方法是一个匹配滤波器，因为它最大化接收到的信号噪声比。然而，匹配滤波器十分需要主用户信号的解调。这意味着，认知无线电有主用户信号的先验知识，在两个PHY和MAC层，例如调制类型和顺序，脉冲整形，报文格式。这样的信息可能被预先存储在认知无线电的记忆模块，但是繁琐的部分是，对于解调，它不得不通过执行定时和载波同步，即使信道均衡，来实现与主用户信号的相干性。这仍然是可能的，因为大多数主要用户具有导频，前导码，同步字或扩散可用于相干检测的代码。举例来说：电视信号为了音频和视频运营商装上了窄带试点，CDMA系统为了飞行员和同步信道装上了扩频码; OFDM包为了数据包采集装上了前导码。匹配滤波器的主要优点是，由于一致性它需要更少的时间，以实现高处理增益，因为只需要O（1/SNR）需要的样品，以满足检测条件约束的给定概率。然而，匹配滤波器的显著缺点是认知无线电将需要一个专用的接收器，用于每一级用户类。
3.
B. Energy Detector
One approach to simplify matched filtering approach is to perform non-coherent detection through energy detection. This sub-optimal technique has been extensively used in radiometry. An energy detector can be implemented similar to a spectrum analyzer by averaging frequency bins of a Fast Fourier Transform (FFT), as outlined in Figure 4.Processing gain is proportional to FFT size N
and observation/averaging time T. Increasing N improves frequency resolution which helps narrowband signal detection. Also, longer averaging time reduces the noise power thus improves SNR. However, due to non-coherent processing O(1/SNR2) samples are required to meet a probability of detection constraint.
B.能量检测
简化匹配滤波的一种方法是通过能量检测来执行非相干检测。这种次优的技术已被广泛地用于辐射。一个能量检测器可以实现类似于用频谱分析仪的功能，通过平均快速傅立叶变换（FFT）的频率箱，如在图4中列出。处理增益和FFT大小N和观察/平均时间T成正比。增加N可以提高频率分辨率，频率分辨率有助于窄带信号检测。另外，较长的平均时间减少了噪声功率从而提高信噪比。然而，由于非相干处理为O（1/SNR2）样本必须符合检测约束的概率。
4.
There are several drawbacks of energy detectors that might diminish their simplicity in implementation. First, a threshold used for primary user detection is highly susceptible to unknown or changing noise levels. Even if the threshold would be set adaptively, presence of any in-band interference would confuse the energy detector. Furthermore, in frequency selective fading it is not clear how to set the threshold with respect to channel notches. Second, energy detector does not differentiate between modulated signals, noise and interference. Since, it cannot recognize the interference, it cannot benefit from adaptive signal processing for canceling the interferer. Furthermore, spectrum policy for using the band is constrained only to primary users, so a cognitive user should treat noise and other secondary users differently. Lastly, an energy detector does not work for spread spectrum signals: direct sequence and frequency hopping signals, for which more sophisticated signal processing algorithms need to be devised. In general, we could increase detector robustness by looking into a primary signal footprint such as modulation type, data rate, or other signal feature.
能量探测器也有一些缺点，可能削弱它实现简单这个特点。首先，用于主用户检测的阈值很容易受到未知的或变化的噪声电平影响。即使阈值将被自适应地设置，任何带内干扰的存在会使能量检测器产生混淆。此外，在频率选择性衰落的时候，不清楚如何相对于信道槽口设置阈值。其次，能量检测器不能把调制信号，噪声和干扰区分开来。由于它不能识别干扰，它不能从自适应信号处理中获益用于消除干扰。此外，对于使用带宽的频谱政策仅仅限于初级用户，所以认知用户应区别对待噪音等二次用户。最后，能量检测器并不用于扩频信号的工作：直接序列和跳频信号，跳频信号是设计出来更复杂的信号处理算法。大体上，我们可以通过寻找到一个主信号足迹例如调制类型，数据速率，或其他信号特征量增加检测的稳健性。
5.
C. Cyclostationary Feature Detection
Modulated signals are in general coupled with sine wave carriers, pulse trains, repeating spreading, hoping sequences, or cyclic prefixes which result in built-in periodicity. Even though the data is a stationary random process, these modulated signals are characterized as cyclostationary, since their statist ics, mean and autocorrelation, exhibit periodicity.This periodicity is typically introduced intentionally in the signal format so that a receiver can exploit it for:parameter estimation such as carrier phase, pulse timing, or direction of arrival. This can then be used for detection of a random signal with a particular modulation type in a background of noise and other modulated signals.
C.循环平稳特征检测
调制信号一般都加上正弦波，脉冲串，重复传播，希望序列，或导致内置的周期性的循环前缀。即使数据是平稳随机过程，这些调制信号的特征为循环平稳，因为它们的统制集成电路，均值和自相关，表现出周期性。这个周期典型引入了已经想好的信号格式，以便接收机可以利用它进行参数估计诸如载波相位，脉冲定时，或到达的方向。这可以被用于检测在噪声和其它的调制信号背景下、特定调制类型的随机信号。
6.
Common analysis of stationary random signals is based on autocorrelation function and power spectral density. On the other hand, cyclostationary signals exhibit correlation between widely separated spectral components due to spectral redundancy caused by periodicity. By analogy with the definition of conventional autocorrelation, one can define spectral correlation function (SCF):
where finite time Fourier transform is given by:
Spectral correlation function is also termed as cyclic spectrum.Unlike PSD which is real-valued one dimensional transform, the SCF is two dimensional transform, in general complex-valued and the parameter αis called cycle frequency. Power spectral density is a special case of a spectral correlation function for α=0.
平稳随机信号的通用分析是基于自相关函数和功率谱密度。另一方面，由于周期性致使的频谱冗余，广泛分离的光谱分量之间循环平稳信号表现出相关性。用类似于传统的自相关的定义，可以定义谱相关函数（SCF）：
其中，有限时间傅立叶变换由下式给出：
谱相关函数也被称为环状频谱.不像PSD是实值的1维变换，SCF是2维变换，一般复值和
参数α被称为循环次数。功率谱密度是一个谱相关函数为α= 0的特殊情况。
7.
The distinctive character of spectral redundancy makes signal selectivity possible. Signal analysis in cyclic spectrum domain preserves phase and frequency information related to timing parameters in modulated signals. As a result, overlapping features in the power spectrum density are non-overlapping feature in the cyclic spectrum. Different types of modulated signals (such as BPSK, QPSK, SQPSK) that have identical power spectral density functions can have highly distinct spectral correlation functions. Furthermore, stationary noise and interference exhibit no spectral correlation.
光谱冗余的独特性使得信号的选择性成为可能。在循环谱域信号分析中，保留与调制信号时序参数相关的相位和频率信息。其结果是，在功率谱密度的重叠特性在循环频谱是非重叠特性。不同类型的调制信号（例如BPSK，DPSK，QPSK），它们都具有相同的功率谱密度函数，可以有高度不同的谱相关函数。此外，平稳噪声和干扰没有表现出谱相关。
8.
Implementation of a spectrum correlation function for cyclostationary feature detection is depicted in Figure 5. It can be designed as augmentation of the energy detector from Figure 4 with a single correlator block. Detected features are number of signals, their modulation types, symbol rates and presence of interferers. Figure 6 illustrates the advantages of cyclostationary detection versus energy detection for continuous phase 4-FSK modulated signals. Distinct pattern of 4-FSK modulation in a spectral correlation function is preserved even in low SNR=-20dB while energy detector is limited by the large noise.
循环平稳特征检测频谱相关函数的实现描绘在图5中。它可被设计为用单个相关模块实现图4中能量检测器的增强。检测到的特征是信号的数字，调制类型，符号率和干扰的存在。图6示出循环平稳检测与能量检测的优势为连续相位4-FSK调制信号。4-FSK调制的谱相关函数不同的图案被保留下来，即使在低信噪比（SNR），20分贝，而能量检测器有大噪声的限制。
9.
Signal processing techniques studied in this paper motivate the need to study other feature detection techniques that can improve sensing detection and recognize modulation, number and type of signals in a low SNR regimes.
本文研究了信号处理技术激励需要研究其他特征检测技术，可以提高感知检测和识别很多不同信号类型的在低信噪比的调制。
附录 科技译文： Numerical Control Numerical Control(NC) is a method of controlling the movements of machineComponents by directly inserting coded instructions in the form of numerical data(numbers and data ) into the system.The system automatically interprets these data and converts to output signals. These signals ,in turn control various machine components ,such as turning spindles on and off ,changing tools,moving the work piece or the tools along specific paths,and turning cutting fluits on and off. In order to appreciate the importer of numerical control of machines ,let’s briefly review how a process such as machining has been carried out traditionally .After studying the working drawing of a part, the operator sets up the appropriate process parameters(such as cutting speed ,feed,depth of cut,cutting fluid ,and so on),determines the sequence of operations to be performed,clamps the work piece in a workholding device such as chuck or collet ,and proceeds to make the part .Depending on part shape and the dimensional accuracy specified ,this approach usually requires skilled
AT89C51的概况 The General Situation of AT89C51 Chapter 1 The application of AT89C51 Microcontrollers are used in a multitude of commercial applications such as modems, motor-control systems, air conditioner control systems, automotive engine and among others. The domains also require that these microcontrollers are be ensured by a robust testing process and a proper tools environment for the validation of these microcontrollers both at the component and at the system level. Intel Plaform Engineering department developed an object-oriented multi-threaded test environment for the validation of its AT89C51 automotive microcontrollers. The goals of thisenvironment was not only to provide a robust testing environment for the AT89C51 automotive microcontrollers, but to develop an environment which can be easily extended and reused for the validation of several other future microcontrollers. The environment was developed in conjunction with Microsoft Foundation Classes (AT89C51). The paper describes the design and mechanism of this test environment, its interactions with various The 8-bit AT89C51 CHMOS microcontrollers are designed to engine-control systems, airbags, suspension systems, and antilock braking systems (ABS). The AT89C51 is especially well suited to applications that benefit from its processing speed and enhanced
外文翻译 专业机械设计制造及其自动化学生姓名刘链柱 班级机制111 学号1110101102 指导教师葛友华
外文资料名称： Design and performance evaluation of vacuum cleaners using cyclone technology 外文资料出处：Korean J. Chem. Eng., 23(6), (用外文写) 925-930 (2006) 附件： 1.外文资料翻译译文 2.外文原文
应用旋风技术真空吸尘器的设计和性能介绍 吉尔泰金，洪城铱昌，宰瑾李， 刘链柱译 摘要：旋风型分离器技术用于真空吸尘器 - 轴向进流旋风和切向进气道流旋风有效地收集粉尘和降低压力降已被实验研究。优化设计等因素作为集尘效率，压降，并切成尺寸被粒度对应于分级收集的50％的效率进行了研究。颗粒切成大小降低入口面积，体直径，减小涡取景器直径的旋风。切向入口的双流量气旋具有良好的性能考虑的350毫米汞柱的低压降和为1.5μm的质量中位直径在1米3的流量的截止尺寸。一使用切向入口的双流量旋风吸尘器示出了势是一种有效的方法，用于收集在家庭中产生的粉尘。 摘要及关键词：吸尘器; 粉尘; 旋风分离器 引言 我们这个时代的很大一部分都花在了房子，工作场所，或其他建筑，因此，室内空间应该是既舒适情绪和卫生。但室内空气中含有超过室外空气因气密性的二次污染物，毒物，食品气味。这是通过使用产生在建筑中的新材料和设备。真空吸尘器为代表的家电去除有害物质从地板到地毯所用的商用真空吸尘器房子由纸过滤，预过滤器和排气过滤器通过洁净的空气排放到大气中。虽然真空吸尘器是方便在使用中，吸入压力下降说唱空转成比例地清洗的时间，以及纸过滤器也应定期更换，由于压力下降，气味和细菌通过纸过滤器内的残留粉尘。 图1示出了大气气溶胶的粒度分布通常是双峰形，在粗颗粒（>2.0微米）模式为主要的外部来源，如风吹尘，海盐喷雾，火山，从工厂直接排放和车辆废气排放，以及那些在细颗粒模式包括燃烧或光化学反应。表1显示模式，典型的大气航空的直径和质量浓度溶胶被许多研究者测量。精细模式在0.18?0.36 在5.7到25微米尺寸范围微米尺寸范围。质量浓度为2?205微克，可直接在大气气溶胶和 3.85至36.3μg/m3柴油气溶胶。
机械设计 摘要：机器是由机械装置和其它组件组成的。它是一种用来转换或传递能量的装置，例如：发动机、涡轮机、车辆、起重机、印刷机、洗衣机、照相机和摄影机等。许多原则和设计方法不但适用于机器的设计，也适用于非机器的设计。术语中的“机械装置设计”的含义要比“机械设计”的含义更为广泛一些，机械装置设计包括机械设计。在分析运动及设计结构时，要把产品外型以及以后的保养也要考虑在机械设计中。在机械工程领域中，以及其它工程领域中，所有这些都需要机械设备，比如：开关、凸轮、阀门、船舶以及搅拌机等。 关键词：设计流程设计规则机械设计 设计流程 设计开始之前就要想到机器的实际性，现存的机器需要在耐用性、效率、重量、速度，或者成本上得到改善。新的机器必需具有以前机器所能执行的功能。 在设计的初始阶段，应该允许设计人员充分发挥创造性，不要受到任何约束。即使产生了许多不切实际的想法，也会在设计的早期，即在绘制图纸之前被改正掉。只有这样，才不致于阻断创新的思路。通常,还要提出几套设计方案，然后加以比较。很有可能在这个计划最后决定中,使用了某些不在计划之内的一些设想。 一般的当外型特点和组件部分的尺寸特点分析得透彻时，就可以全面的设计和分析。接着还要客观的分析机器性能的优越性，以及它的安全、重量、耐用性，并且竞争力的成本也要考虑在分析结果之内。每一个至关重要的部分要优化它的比例和尺寸，同时也要保持与其它组成部分相协调。 也要选择原材料和处理原材料的方法。通过力学原理来分析和实现这些重要的特性，如那些静态反应的能量和摩擦力的最佳利用，像动力惯性、加速动力和能量；包括弹性材料的强度、应力和刚度等材料的物理特性，以及流体润滑和驱动器的流体力学。设计的过程是重复和合作的过程，无论是正式或非正式的进行，对设计者来说每个阶段都很重要。 最后，以图样为设计的标准，并建立将来的模型。如果它的测试是符合事先要
附录 INTEGRATION OF MACHINERY （From ELECTRICAL AND MACHINERY INDUSTRY）ABSTRACT Machinery was the modern science and technology development inevitable result, this article has summarized the integration of machinery technology basic outline and the development background .Summarized the domestic and foreign integration of machinery technology present situation, has analyzed the integration of machinery technology trend of development. Key word：integration of machinery ，technology，present situation ，product t，echnique of manufacture ，trend of development 0. Introduction modern science and technology unceasing development, impelled different discipline intersecting enormously with the seepage, has caused the project domain technological revolution and the transformation .In mechanical engineering domain, because the microelectronic technology and the computer technology rapid development and forms to the mechanical industry seepage the integration of machinery, caused the mechanical industry the technical structure, the product organization, the function and the constitution, the production method and the management system has had the huge change, caused the industrial production to enter into “the integration of machinery” by “the machinery electrification” for the characteristic development phase. 1. Integration of machinery outline integration of machinery is refers in the organization new owner function, the power function, in the information processing function and the control function introduces the electronic technology, unifies the system the mechanism and the computerization design and the software which constitutes always to call. The integration of machinery development also has become one to have until now own system new discipline, not only develops along with the science and technology, but also entrusts with the new content .But its basic characteristic may summarize is: The integration of machinery is embarks from the system viewpoint, synthesis community technologies and so on utilization mechanical technology, microelectronic technology, automatic control technology,
毕业设计（论文）外文文献翻译 文献、资料中文题目：软件开发概念和设计方法文献、资料英文题目： 文献、资料来源： 文献、资料发表（出版）日期： 院（部）： 专业： 班级： 姓名： 学号： 指导教师： 翻译日期： 2017.02.14
外文资料原文 Software Development Concepts and Design Methodologies During the 1960s, ma inframes and higher level programming languages were applied to man y problems including human resource s yste ms,reservation s yste ms, and manufacturing s yste ms. Computers and software were seen as the cure all for man y bu siness issues were some times applied blindly. S yste ms sometimes failed to solve the problem for which the y were designed for man y reasons including: ?Inability to sufficiently understand complex problems ?Not sufficiently taking into account end-u ser needs, the organizational environ ment, and performance tradeoffs ?Inability to accurately estimate development time and operational costs ?Lack of framework for consistent and regular customer communications At this time, the concept of structured programming, top-down design, stepwise refinement，and modularity e merged. Structured programming is still the most dominant approach to software engineering and is still evo lving. These failures led to the concept of "software engineering" based upon the idea that an engineering-like discipl ine could be applied to software design and develop ment. Software design is a process where the software designer applies techniques and principles to produce a conceptual model that de scribes and defines a solution to a problem. In the beginning, this des ign process has not been well structured and the model does not alwa ys accurately represent the problem of software development. However,design methodologies have been evolving to accommo date changes in technolog y coupled with our increased understanding of development processes. Whereas early desig n methods addressed specific aspects of the
使用高级分析法的钢框架创新设计 1．导言 在美国，钢结构设计方法包括允许应力设计法(ASD)，塑性设计法(PD)和荷载阻力系数设计法(LRFD)。在允许应力设计中，应力计算基于一阶弹性分析，而几何非线性影响则隐含在细部设计方程中。在塑性设计中，结构分析中使用的是一阶塑性铰分析。塑性设计使整个结构体系的弹性力重新分配。尽管几何非线性和逐步高产效应并不在塑性设计之中，但它们近似细部设计方程。在荷载和阻力系数设计中，含放大系数的一阶弹性分析或单纯的二阶弹性分析被用于几何非线性分析，而梁柱的极限强度隐藏在互动设计方程。所有三个设计方法需要独立进行检查，包括系数K计算。在下面，对荷载抗力系数设计法的特点进行了简要介绍。 结构系统内的内力及稳定性和它的构件是相关的，但目前美国钢结构协会（AISC）的荷载抗力系数规范把这种分开来处理的。在目前的实际应用中，结构体系和它构件的相互影响反映在有效长度这一因素上。这一点在社会科学研究技术备忘录第五录摘录中有描述。 尽管结构最大内力和构件最大内力是相互依存的（但不一定共存），应当承认，严格考虑这种相互依存关系，很多结构是不实际的。与此同时，众所周知当遇到复杂框架设计中试图在柱设计时自动弥补整个结构的不稳定（例如通过调整柱的有效长度）是很困难的。因此，社会科学研究委员会建议在实际设计中，这两方面应单独考虑单独构件的稳定性和结构的基础及结构整体稳定性。图28.1就是这种方法的间接分析和设计方法。
在目前的美国钢结构协会荷载抗力系数规范中，分析结构体系的方法是一阶弹性分析或二阶弹性分析。在使用一阶弹性分析时，考虑到二阶效果，一阶力矩都是由B1,B2系数放大。在规范中，所有细部都是从结构体系中独立出来，他们通过细部内力曲线和规范给出的那些隐含二阶效应，非弹性，残余应力和挠度的相互作用设计的。理论解答和实验性数据的拟合曲线得到了柱曲线和梁曲线，同时Kanchanalai发现的所谓“精确”塑性区解决方案的拟合曲线确定了梁柱相互作用方程。 为了证明单个细部内力对整个结构体系的影响，使用了有效长度系数，如图28.2所示。有效长度方法为框架结构提供了一个良好的设计。然而，有效长度方法的
中英文资料对照外文翻译 机械设计 摘要： 机器由机械和其他元件组成的用来转换和传输能量的装置。比如：发动机、涡轮机、车、起重机、印刷机、洗衣机和摄影机。许多机械方面设计的原则和方法也同样适用于非机械方面。术语中的“构造设计”的含义比“机械设计”更加广泛，构造设计包括机械设计。在进行运动分析和结构设计时要把产品的维护和外形也考虑在机械设计中。在机械工程领域中，以及其它工程领域，都需要机械设备，比如：开关、凸轮、阀门、船舶以及搅拌机等。 关键词：设计流程设计规则机械设计 设计流程 设计开始之前就要想到机器的实用性，现有的机器需要在耐用性、效率、重量、速度，或者成本上得到改善。新的机器必需能够完全或部分代替以前人的功能，比如计算、装配、维修。 在设计的初级阶段，应该充分发挥设计人员的创意，不要受到任何约束。即使有一些不切实际的想法，也可以在设计的早期，即在绘制图纸之前被改正掉。只有这样，才不致于阻断创新的思路。通常,必须提出几套设计方案,然后进行比较。很有可能在这个计划最后指定使用某些不在计划方案内的一些想法的计划。 一般当产品的外型和组件的尺寸特点已经显现出来的时候，就可以进行全面的设计和分析。接着还要客观的分析机器性能、安全、重量、耐用性，并且成本也要考虑在内。每一个至关重要的部分要优化它的比例和尺寸，同时也要保持与其它组成部分的平衡。 选择原材料和工艺的方法。通过力学原理来分析和实现这些重要的特性，如稳定和反应的能量和摩擦力的利用，动力惯性、加速度、能量；包括材料的弹性强度、应力和刚度等物理特性，以及流体的润滑和驱动器的流体力学。设计的过程是一个反复与合作的过程，无论是正式的还是非正式的，对设计者来说每个阶段都很重要。。产品设计需要大量的研究和提升。许多的想法,必须通过努力去研究成为一种理念,然后去使用或放弃。
本科毕业论文(设计) 外文翻译 学院：机电工程学院 专业：机械工程及自动化 姓名：高峰 指导教师：李延胜 2011年05 月10日 教育部办公厅 Failure Analysis，Dimensional Determination And
Analysis，Applications Of Cams INTRODUCTION It is absolutely essential that a design engineer know how and why parts fail so that reliable machines that require minimum maintenance can be designed．Sometimes a failure can be serious，such as when a tire blows out on an automobile traveling at high speed．On the other hand，a failure may be no more than a nuisance．An example is the loosening of the radiator hose in an automobile cooling system．The consequence of this latter failure is usually the loss of some radiator coolant，a condition that is readily detected and corrected．The type of load a part absorbs is just as significant as the magnitude．Generally speaking，dynamic loads with direction reversals cause greater difficulty than static loads，and therefore，fatigue strength must be considered．Another concern is whether the material is ductile or brittle．For example，brittle materials are considered to be unacceptable where fatigue is involved． Many people mistakingly interpret the word failure to mean the actual breakage of a part．However，a design engineer must consider a broader understanding of what appreciable deformation occurs．A ductile material，however will deform a large amount prior to rupture．Excessive deformation，without fracture，may cause a machine to fail because the deformed part interferes with a moving second part．Therefore，a part fails(even if it has not physically broken)whenever it no longer fulfills its required function．Sometimes failure may be due to abnormal friction or vibration between two mating parts．Failure also may be due to a phenomenon called creep，which is the plastic flow of a material under load at elevated temperatures．In addition，the actual shape of a part may be responsible for failure．For example，stress concentrations due to sudden changes in contour must be taken into account．Evaluation of stress considerations is especially important when there are dynamic loads with direction reversals and the material is not very ductile． In general，the design engineer must consider all possible modes of failure，which include the following． ——Stress ——Deformation ——Wear ——Corrosion ——Vibration ——Environmental damage ——Loosening of fastening devices
机械设计理论 机械设计是一门通过设计新产品或者改进老产品来满足人类需求的应用技术科学。它涉及工程技术的各个领域，主要研究产品的尺寸、形状和详细结构的基本构思，还要研究产品在制造、销售和使用等方面的问题。 进行各种机械设计工作的人员通常被称为设计人员或者机械设计工程师。机械设计是一项创造性的工作。设计工程师不仅在工作上要有创造性，还必须在机械制图、运动学、工程材料、材料力学和机械制造工艺学等方面具有深厚的基础知识。如前所诉，机械设计的目的是生产能够满足人类需求的产品。发明、发现和科技知识本身并不一定能给人类带来好处，只有当它们被应用在产品上才能产生效益。因而，应该认识到在一个特定的产品进行设计之前，必须先确定人们是否需要这种产品。 应当把机械设计看成是机械设计人员运用创造性的才能进行产品设计、系统分析和制定产品的制造工艺学的一个良机。掌握工程基础知识要比熟记一些数据和公式更为重要。仅仅使用数据和公式是不足以在一个好的设计中做出所需的全部决定的。另一方面，应该认真精确的进行所有运算。例如，即使将一个小数点的位置放错，也会使正确的设计变成错误的。 一个好的设计人员应该勇于提出新的想法，而且愿意承担一定的风险，当新的方法不适用时，就使用原来的方法。因此，设计人员必须要有耐心，因为所花费的时间和努力并不能保证带来成功。一个全新的设计，要求屏弃许多陈旧的，为人们所熟知的方法。由于许多人墨守成规，这样做并不是一件容易的事。一位机械设计师应该不断地探索改进现有的产品的方法，在此过程中应该认真选择原有的、经过验证的设计原理，将其与未经过验证的新观念结合起来。 新设计本身会有许多缺陷和未能预料的问题发生，只有当这些缺陷和问题被解决之后，才能体现出新产品的优越性。因此，一个性能优越的产品诞生的同时，也伴随着较高的风险。应该强调的是，如果设计本身不要求采用全新的方法，就没有必要仅仅为了变革的目的而采用新方法。 在设计的初始阶段，应该允许设计人员充分发挥创造性，不受各种约束。即使产生了许多不切实际的想法，也会在设计的早期，即绘制图纸之前被改正掉。只有这样，才不致于堵塞创新的思路。通常，要提出几套设计方案，然后加以比较。很有可能在最后选定的方案中，采用了某些未被接受的方案中的一些想法。
沈阳工业大学工程学院 毕业设计（论文）外文翻译 毕业设计（论文）题目：工具盒盖注塑模具设计 外文题目：Friction , Lubrication of Bearing 译文题目：轴承的摩擦与润滑 系（部）：机械系 专业班级：机械设计制造及其自动化0801 学生姓名：王宝帅 指导教师：魏晓波 2010年10 月15 日
外文文献原文： Friction , Lubrication of Bearing In many of the problem thus far , the student has been asked to disregard or neglect friction . Actually , friction is present to some degree whenever two parts are in contact and move on each other. The term friction refers to the resistance of two or more parts to movement. Friction is harmful or valuable depending upon where it occurs. friction is necessary for fastening devices such as screws and rivets which depend upon friction to hold the fastener and the parts together. Belt drivers, brakes, and tires are additional applications where friction is necessary. The friction of moving parts in a machine is harmful because it reduces the mechanical advantage of the device. The heat produced by friction is lost energy because no work takes place. Also , greater power is required to overcome the increased friction. Heat is destructive in that it causes expansion. Expansion may cause a bearing or sliding surface to fit tighter. If a great enough pressure builds up because made from low temperature materials may melt. There are three types of friction which must be overcome in moving parts: (1)starting, (2)sliding, and(3)rolling. Starting friction is the friction between two solids that tend to resist movement. When two parts are at a state of rest, the surface irregularities of both parts tend to interlock and form a wedging action. To produce motion in these parts, the wedge-shaped peaks and valleys of the stationary surfaces must be made to slide out and over each other. The rougher the two surfaces, the greater is starting friction resulting from their movement . Since there is usually no fixed pattern between the peaks and valleys of two mating parts, the irregularities do not interlock once the parts are in motion but slide over each other. The friction of the two surfaces is known as sliding friction. As shown in figure ,starting friction is always greater than sliding friction . Rolling friction occurs when roller devces are subjected to tremendous stress which cause the parts to change shape or deform. Under these conditions, the material in front of a roller tends to pile up and forces the object to roll slightly uphill. This changing of shape , known as deformation, causes a movement of molecules. As a result ,heat is produced from the added energy required to keep the parts turning and overcome friction. The friction caused by the wedging action of surface irregularities can be overcome
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。 指导教师评语： 该生外文翻译没有基本的语法错误，用词准确，没 有重要误译，忠实原文；译文通顺，条理清楚，数量与 质量上达到了本科水平。 签名： 年月日 注：请将该封面与附件装订成册。
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。当32位设备是传送目标时，ACK64#不能漂移。 ●AD[64::32]包含上部4位地址／数据通道。 ●C/BE#[7::4]包含高4位命令/字节使能信号。 ●PAR64是为上部4个AD通道和上部4位C/BE信号线提供偶校验的奇偶校验位。 以下是几小结详细讨论64位数据传送和寻址功能。 3.在32位插入式连接器上的64位卡
理工学院毕业设计(论文)外文资料翻译 专业：热能与动力工程 姓名：赵海潮 学号：09L0504133 外文出处：Applied Acoustics, 2010(71):701~707 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 基于一维CFD模型下汽车排气消声器的实验研究与预测Takeshi Yasuda, Chaoqun Wua, Noritoshi Nakagawa, Kazuteru Nagamura 摘要目前，利用实验和数值分析法对商用汽车消声器在宽开口喉部加速状态下的排气噪声进行了研究。在加热工况下发动机转速从1000转/分钟加速到6000转/分钟需要30秒。假定其排气消声器的瞬时声学特性符合一维计算流体力学模型。为了验证模拟仿真的结果，我们在符合日本工业标准（JIS D 1616）的消声室内测量了排气消声器的瞬态声学特性，结果发现在二阶发动机转速频率下仿真结果和实验结果非常吻合。但在发动机高阶转速下（从5000到6000转每分钟的四阶转速，从4200到6000转每分钟的六阶转速这样的高转速范围内），计算结果和实验结果出现了较大差异。根据结果分析，差异的产生是由于在模拟仿真中忽略了流动噪声的影响。为了满足市场需求，研究者在一维计算流体力学模型的基础上提出了一个具有可靠准确度的简化模型，相对标准化模型而言该模型能节省超过90％的执行时间。 关键字消声器排气噪声优化设计瞬态声学性能 1 引言 汽车排气消声器广泛用于减小汽车发动机及汽车其他主要部位产生的噪声。一般而言，消声器的设计应该满足以下两个条件：（1）能够衰减高频噪声，这是消声器的最基本要求。排气消声器应该有特定的消声频率范围，尤其是低频率范围，因为我们都知道大部分的噪声被限制在发动机的转动频率和它的前几阶范围内。（2）最小背压，背压代表施加在发动机排气消声器上额外的静压力。最小背压应该保持在最低限度内，因为大的背压会降低容积效率和提高耗油量。对消声器而言，这两个重要的设计要求往往是互相冲突的。对于给定的消声器，利用实验的方法，根据距离尾管500毫米且与尾管轴向成45°处声压等级相近的排气噪声来评估其噪声衰减性能，利用压力传感器可以很容易地检测背压。 近几十年来，在预测排气噪声方面广泛应用的方法有：传递矩阵法、有限元法、边界元法和计算流体力学法。其中最常用的方法是传递矩阵法（也叫四端网络法）。该方
机械设计理论 The machine design theory The machine design is through designs the new product or improves the old product to meet the human need the application technical science. It involves the project technology each domain, mainly studies the product the size, the shape and the detailed structure basic idea, but also must study the product the personnel which in aspect the and so on manufacture, sale and use question. Carries on each kind of machine design work to be usually called designs the personnel or machine design engineer. The machine design is a creative work. Project engineer not only must have the creativity in the work, but also must in aspect and so on mechanical drawing, kinematics, engineerig material, materials mechanics and machine manufacture technology has the deep elementary knowledge. If front sues, the machine design goal is the production can meet the human need the product. The invention, the discovery and technical knowledge itself certainly not necessarily can bring the advantage to the humanity, only has when they are applied can produce on the product the benefit. Thus, should realize to carries on before the design in a specific product, must first determine whether the people do need this kind of product Must regard as the machine design is the machine design personnel carries on using creative ability the product design, the system analysis and a formulation product manufacture technology good opportunity. Grasps the project elementary knowledge to have to memorize some data and the formula is more important than. The merely service data and the formula is insufficient to the completely decision which makes in a good design needs. On the other hand, should be earnest precisely carries on all operations. For example, even if places wrong a decimal point position, also can cause the correct design to turn wrongly.