通信与电子信息科技英语 总ppt课件

ity of a random process in
the same way.
Exercises
6. It is of interest to inquire whether G(f) defined in Eq. (1.2) for a random process has a physical significance whichcorresponds to the physical significance of G(f) for deterministic waveforms. 8. Hence, if we should select some sample function, a knowledge of the value of n(t) at time t would be of no assistance in improving our ability to predict the value attained by that same sample function at time t+τ. 9. Hence,whenever we make an observation or measurement of the pulse waveform which extends over a duration long enough so that the average observed pulse shape,such as their amplitudes,widths,and spacings are representative of the waveform generally,we shall find that Eq.(1.12)applies.
Exercises
6. The signal is transmitted in a channel which can be represented as a lowpass RC circuit with cutoff at 1 Hz. 7. If there is no noise, then we are entirely free to make as for the attenuation by the use of an amplifier and to correct the frequency distortion by the use of an equalizer. 8. That is, we need to estimate the interval T which should be assigned to each message to allow the transmitted levels to be recognized Individually over the receiver, even though the bandwidth B of the channel is limited. 9. Therefore, the 25 percent reduction in bandwidth requires a 60 percent increase of signal power.
Exercises
10. While we have used the term communication channel in many occasions, it is well to emphasize at this point, that the term, which is Something as an abstraction, is intended to encompass all the features and componentparts of the transmission system which introduce noise or limit the bandwidth. 11. The probability of error is close to unity for every possible set of M transmitter signals. 12. It turns out that the results obtained for a gaussian channel often provide a lower bound in the performance of a system Operating in a nongaussian channel.
11. 信道容量 12. 13. 误码率 14. 15. 限带高斯信道 16.
Exercises
channel capacity Two sided power spectral density error probability (probability of error) Nyquist sampling rate band limited gaussian channel white Gaussian noise
样本函数 总体均值 物理意义
傅立叶变换对 确定性波型
在极限情况下 时不变的 频率上限
巴塞瓦尔定理
随机脉冲
Exercises
Ⅱ. Please translate the following words and
phrases into English.
1. 随机过程 2. 3. 随机变量
random process statistical average
Exercises
10. Let us select a section of this waveform which extends from-
T/2
to -T/2.
11. Since we have assumed an ergodic process,we are at liberty to
phrases into English.
1. 通信理论 2. 3. 信道带宽 4. 5. 理想低通滤波器 6. 7. 无噪声高斯信道 8. 9. 信息速率 10.
communication theory(theory of communications) Shannon’s theorem channel bandwidth signal waveform ideal lowpass filter autocorrelation function noiseless gaussian channel communication channel information rate Signal to noise ratio（SNR,S/N）
均方根值, 均方根；均方根(的)
8. trade off 9. lower bound
下界, 下限
1. equalizer 11. vice versa 12. upper limit
反之亦然 上限
Exercises
Ⅱ. Please translate the following words and
Function at successive times will yield a time average, which we
represent as n2(t1).
3. Suppose, for example, that the statistical characteristics of the sample Functions in the ensemble were changing with time.
and phrases into Chinese.
1. physical syste
物理系统，实际系统
2. rise time 3. amount of information
信息量
4. in principle 5. gaussian channel
高斯信道
6. probability density 7. root mean square
4. For it may happen that while each sample function is stationary the in dividual sample functions may differ statistically from one another.
5. As an extension of that result we shall define the power spectral dens
Exercises
Ⅲ. Fill in the blanks with the missing word(s).
1.There is a negative statement associated with Shannon’s theorem.
2. on the purpose of transmission over the channel, the messages are represented by fixed voltage levels. 3. Since the transmission of any of the M messages is equally likely,H=log2M,thus our channel is transferring information at a rate R=rH. 4. For a fixed signal power and in the presence of white gaussian noise the channel capacity approaches an upper limit with increasing bandwidth. 5. It is of great interest to recognize that the tradeoff between bandwidth and signal to noise ratio is not limited by a lower limit in bandwidth.
Exercises
Ⅲ. Fill in the blanks with the missing
word(s).
1. The ensemble averages will be identical with the statistical averages
and may be represented by the same symbols. 2. The averages determined by measurements on a single sample
perform (perform, performing) the averaging over any sample
function of the ensemble, since every sample function will yield the same
result.
Exercises
Ⅰ. Please translate the following words
a stationary process statistical态历经过程 14. 狄拉克函数
time average statistical characteristic
ergodic process delta function
random variable
4.
autocorrelation function
5. 傅里叶变换
Fourier transform
6.
power spectral density
7. 概率密度函数 8. 9. 平稳过程 10.
probability density function
gaussian process
Exercises
Ⅰ. Please translate the following words and phrases
into Chinese.
1. sample function 2. ensemble average 3. physical significance 4. a Fourier transform pair 5. deterministic waveform 6. in the limit 7. time invariant 8. an upper frequency limit 9. Parseval’s theorem 10. random pulses