Engineering Exam代考：ELEN30012 Signals and Systems

信号是携带数据的电流或电磁电流，可以传输或接收。

在数学上表示为自变量的函数，例如密度、深度等。因此，信号是随时间、空间或可以传达信息的任何其他自变量而变化的物理量。这里的自变量是时间。

时间信号的类型：

连续时间信号 x(t)-在每个时间点定义

离散时间信号 x[n] –仅在一组离散的时间值（整数）处定义。

系统是任何一组物理组件或多个设备的功能，它们将信号输入并产生信号作为输出。

模拟信号

信号可以是模拟量，这意味着它是根据时间定义的。这是一个连续的信号。这些信号是在连续自变量上定义的。它们很难分析，因为它们带有大量的值。由于大量的值样本，它们非常准确。为了存储这些信号，您需要无限的内存，因为它可以在实线上实现无限的值。模拟信号用正弦波表示。

数字信号

与模拟信号相比，数字信号非常容易分析。它们是不连续的信号。它们是模拟信号的挪用。

数字这个词代表离散值，因此这意味着它们使用特定值来表示任何信息。在数字信号中，只有两个值用于表示某事，即：1 和 0（二进制值）。数字信号不如模拟信号准确，因为它们是在一段时间内获取的模拟信号的离散样本。然而，数字信号不受噪声影响。因此它们持续时间长且易于解释。数字信号用方波表示。

模拟信号和数字信号的区别

比较元素	模拟信号	数字信号
分析	难的	可分析
表示	连续的	不连续
准确性	更准确的	不太准确
贮存	无限记忆	易于存储
受噪音影响	是的	不
录音技术	保留原始信号	采集并保存信号样本
例子	人声、温度计、模拟电话等	电脑、数码电话、数码笔等

信号与系统的代写高分代写案例

Question 1

• I am a non-zero continuous-time signal x. When you use me as an input signal to a stable linear time-invariant system then the output signal will be myself times a constant complex number. Who am I? Explain your answer-but no proofs are needed.
• Consider a continuous-time system given by the equation

y ⑴=sin(tXt),

where v denotes the input signal and y denotes the output signal.

1. Is this system linear time-invariant? If “no”, which property is miss­ing: “linearity” or “time-invariance”, or both——explain your answers. If “yes”, give a proof.
2. Consider the response y to the input signal v given by v(t) = cost Show that y can be expressed as = 6cos(u；of — </>), where b,必 and <p are positive real numbers and where (p < 2兀；be sure to give the numerical values of b, and 0.
3. Explain how your answer in (ii) can be used to answer (i).
4. Consider an ideal filter with frequency response

1        0 < |cu| <

0 otherwise ‘

where 3c is a positive real number. Consider the output signal y that is the response of this filter to the periodic input signal v from part (b). For S =开/3 it can be shown that the signal y can be written as

y(t) = & + K2cos(δ)，

where K? and a are real numbers. Determine K]，K2 and a.

• Repeat (c) for = tt/8.
• Repeat (c) for lj_c = 2tt/3.
• [Consider the wave w given by

oo

w(t) = g[t — 81) for all i G R,

1——OQ

with g defined for alU 6 R as

W = J        ⁴             -2 < t < 0

0         [    0            otherwise.

Repeat part (b) for this wave w.

• Which of the following discrete lime signals are periodic? No explanations are needed; there can be zero, one or more than one answer.
• x[n) = cos(7rn)
• x(n) – cos(n\/5)
• x(n) — cos(n\/5) + cos(7T7i)
• x(n) — cos(n\/5) + cos(2n\/5)
• Which of the following continuous time signals are periodic? No expla­nations are needed; there can be zero, one or more than one answer.
• x(t) = C0S(7Tf)
• x(t) = cos(t\/5)
• x(t) = cos(t\/5) + cos(7rt)
• x(t) = cos(t\/5) + cos(2t\/5)

Question 2

In this question 6 denotes the discrete-time unit pulse signal:

J(n) = |                       [0 otherwise.

• 11 mark] Consider the discrete-time signal x, defined for all n e Z, given by

_x(_n\ = J ¹                 九=123

[0         otherwise.

Further define the discrete-time signal y by

y(n) = x(n) + x(—n) + d(n).

Sketch y and make sure that you indicate relevant values in your plot.

• Plot the signal where denotes discrete-time convolution and x and y are as in (a). Make sure that you indicate relevant values in your plot.
• Let x be as in part (a). Consider the system that has x as its unit pulse response. Compute the system’s step response.