东南大学数字通信期末试卷04-05(附答案)

diversity，
diversity，
diversity.
5. 5. Three major sources of degradation in wireless communications
are
院 ,
, and
; the latter
学 心 two are byproducts of multipath.
息 中 6. 6. The information capacity of a continuous channel of bandwidth B
信 辅导 hertz, perturbed by additive white Gaussian noise of power spectral
信 辅 the channel but also on the way in which the channel used. 学习 6. 6. Shannon’s second theorem specifies the channel capacity C as a
fundamental limit on the rate at which the transmission of reliable error-free messages can take place over a discrete memoryless channel and how to construct a good code. 7. 7. The syndrome depends not only on the error pattern, but also on the transmitted code word. 8. 8. Any pair of primitive polynomials of degree m whose corresponding shift registers generate m-sequences of period 2m-1 can be used to generate a Gold sequence. 9. 9. Any source code satisfies the Kraft-McMillan inequality can be a prefix code. 10. 10. Let a discrete memoryless source with an alphabet ϕ have entropy H (ϕ) and produce symbols once every Ts seconds. Let a discrete memoryless channel have capacity C and be used once every Tc
2. 2. For a period of the maximal-length sequence, the autocorrelation function is similar to that of a random binary wave.
3. 3. For slow-frequency hopping，symbol rate Rs of MFSK signal is an integer multiple of the hop rate Rh. That is, the carrier frequency will change or hop several times during the transmission of one symbol.
Section B：Fill in the blanks （35%）
1. 1. The two commonly used types of spread-Baidu Nhomakorabeapectrum modulation:
and
.
2. 2. A pseudo-noise (PN) sequence is a periodic binary sequence with a
waveform that is usually generated by means of a
.
3. 3. Due to
, wireless communication is no longer
idealized AWGN channel model.
4. 4. There are the following diversity techniques in our discussion ，
H (ϕ) ≥ C seconds. Then , if Ts Tc , there exists a coding scheme for which the source output can be transmitted over the channel and be reconstructed with an arbitrarily small probability of error.
东 南 大 学 考 试 卷 (A 卷 )
课程名称 数 字 通 信
考 试 学 期 0 4 - 0 5 - 2 得分
适 用 专 业 无线电工程系 考 试 形 式 闭 卷 考 试 时 间 长 度 120 分钟 共 页
Section A：True or False （15%）
1. 1. When the period is exactly 2m, the PN sequence is called a maximal-length-sequence or simply m-sequence.
4. 4. Frequency diversity can be done by choosing a frequency spacing
学院 心 equal to or less than the coherence bandwidth of the channel. 息 导中 5. 5. The mutual information of a channel therefore depends not only on