1、宁波大学宁波大学 2015 年攻读年攻读博博士学位研究生士学位研究生 入入 学学 考考 试试 试试 题题(B 卷卷) (答案必须写在答题纸上) 考试科目考试科目: 数字通信数字通信 科目代码：科目代码： 3807 适用专业适用专业: 通信与信息系统通信与信息系统/信号与信息处理信号与信息处理/移动计算与人机交互移动计算与人机交互/微纳信息系统微纳信息系统 第 1 页 共 4 页 一、填空（16 分） 1、QAM 信号的解调通常采用（ ）相干解调。 2、设在s125内传输 256 个二进制码元，则码元传输速率是（ ）。 3、如果理想 MPSK 数字调制传输系统的带宽为 10kHz，则该系统无码间
2、干扰最大信息传输速率为（ ）b/s。 4、数字通信系统的有效性指标有（ ）和（ ），可靠性指标有（ ）。 5、数字通信的任务是（ ）、（ ）地传递信息。 二、选择题（14 分） 从下面所列答案中选择出最合理的答案，填入后面的答题中。每个空格只能选一个答案，不排除某一个答案被多次选择的可能性。 示例题：3+2= （ p ）， 2 0= （ k ） (a) 2DPSK (b) 2ASK (c) 2PSK (d) 2FSK (e) 慢 (f)快 (g) 倒现象 (h) 相位错移 (i) kb/slog2M (j) kb/slog102M (k) 0 (l) 2 (m) 时域均衡 (n) 循环稳定 (
3、o) 高 (p)5 1、BPSK 信号在接收端因为载波同步系统中的分频，可能产生载波相位状态转移，发生对信号的错误解调，这种现象称为（ ）。 2、对于传输信道所引入的码间干扰，一种基本的解决方法是采用（ ）。 3、如果升余弦滚降系统的滚降系数越小，则相应的系统总的冲激响应 x (t)的拖尾衰减越（ ）。 4、2DPSK，2ASK，2PSK，2FSK，采用相干解调时，抗信道加性高斯白噪声性能从好到坏排列顺序是（ ），（ ），（ ），（ ）。 宁波大学宁波大学 2015 年攻读年攻读博博士学位研究生士学位研究生 入入 学学 考考 试试 试试 题题(B 卷卷) (答案必须写在答题纸上) 考试科目考试
4、科目: 数字通信数字通信 科目代码：科目代码： 3807 适用专业适用专业: 通信与信息系统通信与信息系统/信号与信息处理信号与信息处理/移动计算与人机交互移动计算与人机交互/微纳信息系统微纳信息系统 第 2 页 共 4 页 三、计算题（10 分） （1）设某个数字通信传输系统的二进制独立等概率信号的码元宽度为 0.5ms，求该数字通信传输系统的码元速率BR和信息速率bR； （2）如果将该数字通信传输系统改为传送四进制信号，假设其码元带宽不变，则此时该数字通信传输系统的码元速率BR和信息速率bR是多少？ 四、Translate the following from English into C
5、hinese. And，say something about your understanding of digital communications, communication system, or information system. (60 分) Orthogonal frequency division multiplexing (OFDM) has become a popular technique for transmission of signals over wireless channels. OFDM has been adopted in several wire
6、less standards such as digital audio broadcasting (DAB), digital video broadcasting (DVB-T), the IEEE 802.11a local area network (LAN) standard and the IEEE 802.16a metropolitan area network (MAN) standard. OFDM is also being pursued for dedicated short-range communications (DSRC) for road side to v
7、ehicle communications and as a potential candidate for fourth-generation (4G) mobile wireless systems. OFDM converts a frequency-selective channel into a parallel collection of frequency flat subchannels. The subcarriers have the minimum frequency separation required to maintain orthogonality of the
8、ir corresponding time domain waveforms, yet the signal spectra corresponding to the different subcarriers overlap in frequency. Hence, the available bandwidth is used very efficiently. If knowledge of the channel is available at the transmitter, then the OFDM transmitter can adapt its signaling stra
9、tegy to match the channel. Due to the fact that OFDM uses a large collection of narrowly spaced subchannels, these adaptive strategies can approach the ideal water pouring capacity of a frequency selective channel. OFDM is a block modulation scheme where a block of information symbols is transmitted
10、 in parallel on subcarriers. The time duration of an OFDM symbol is times larger than that of a single carrier system. An OFDM modulator can be implemented as an inverse discrete Fourier transform (IDFT) on a block of information symbols followed by an analog-to-digital converter (ADC). To mitigate
11、the effects of inter-symbol interference (ISI) caused by channel time spread, each block of IDFT coefficients is typically preceded by a cyclic prefix (CP) or a guard interval consisting of samples, such that the length of the CP is at least equal to the channel length. Under this condition, a linea
12、r convolution of the transmitted sequence and the channel is converted to a circular convolution. As a result, the effects of the ISI are easily and completely eliminated. Moreover, the approach enables the receiver to use fast signal processing transforms such as a fast Fourier transform (FFT) for
13、OFDM implementation. Similar techniques can be employed in single-carrier systems as well, by preceding each transmitted data block of length by a CP of length , while using frequency domain equalization at the receiver. While the first mobile communications standards focused primarily on voice comm
14、unication, the 宁波大学宁波大学 2015 年攻读年攻读博博士学位研究生士学位研究生 入入 学学 考考 试试 试试 题题(B 卷卷) (答案必须写在答题纸上) 考试科目考试科目: 数字通信数字通信 科目代码：科目代码： 3807 适用专业适用专业: 通信与信息系统通信与信息系统/信号与信息处理信号与信息处理/移动计算与人机交互移动计算与人机交互/微纳信息系统微纳信息系统 第 3 页 共 4 页 emphasis now has returned to the provision of systems optimized for data. This trend began wit
15、h the 3rd Generation Wideband Code Division Multiple Access (WCDMA) system designed in the 3GPP, and is now reaching fulfilment in its successor, known as the Long-Term Evolution (LTE). LTE is the first cellular communication system optimized from the outset to support packet-switched data services,
16、 within which packetized voice communications are just one part. LTE is an enabler. It is not technology for technologys sake, but technology with a purpose, connecting people and information to enable greater things to be achieved. It will provide higher data rates than ever previously achieved in
17、mobile communications, combined with wide-area coverage and seamless support for mobility without regard for the type of data being transmitted. The fourth generation (4G) of wireless cellular systems has been a topic under discussion for a long time, probably since the formal definition of third ge
18、neration (3G) cellular systems was completed by the International Telecommunications Union (ITU) in 1997. Upon completing the development of the 3G family of standards, the Third Generation Partnership Project (3GPP) started working on Long Term Evolution (LTE) systems during the Release 8 (Rel-8) o
19、f the standards. Being the first cellular system based on Orthogonal Frequency Division Multiple Access (OFDMA), it represented a major breakthrough in terms of achieving peak data rates of 300 Mbps in the downlink. However, both LTE Rel-8 and Rel-9 specifications did not meet the IMT-Advanced requi
20、rements established by the ITU for 4G systems. LTE-Advanced, the first accepted 4G system whose standardization was initiated in Rel-10 by 3GPP, was born as the resulting efforts of 3GPP to meet those requirements. Major performance goals included peak rates of 1 Gbps in the downlink and 500 Mbps in
21、 the uplink. However, current predictions for future systems point out tremendous challenges far beyond what the ITU initially established for 4G. Driven by both the explosion of users demands for mobile data along with new services and applications, and the need for a ubiquitous and wirelessly acce
22、ssible cloud platform, the evolution of future mobile traffic is expected to boom. Applications and services demand ever-increasing data rates. A traffic growth of up to 30 times has been predicted to take place between the years 2010 and 2015. By 2016, more than 10 exabytes of traffic per month wil
23、l be circulating across cellular networks and more than 4 billion 3GPP wireless subscriptions will be operating in the network. With these forecasts in mind, it becomes critical to provide not only very high broadband capacity, but also efficient support for a variety of traffic types, flexible and
24、cost efficient deployments, energy efficient communications strategies, robust systems against emergencies, and a balance between backward compatibility and future enhancements. The standardization of LTE became one of the most important technology shifts in cellular networks since the introduction
25、of WCDMA. However, it was not until the introduction of LTE-Advanced in Rel-10 that the requirements established by the ITU for 4G technologies were finally achieved. Nevertheless, both industry and academia have continued improving LTE-Advanced through enhancements in the core technologies of carri
26、er aggregation, MIMO, relaying, and cooperative multipoint communications. In addition, in order to cope with the ever increasing demand for 宁波大学宁波大学 2015 年攻读年攻读博博士学位研究生士学位研究生 入入 学学 考考 试试 试试 题题(B 卷卷) (答案必须写在答题纸上) 考试科目考试科目: 数字通信数字通信 科目代码：科目代码： 3807 适用专业适用专业: 通信与信息系统通信与信息系统/信号与信息处理信号与信息处理/移动计算与人机交互移动计
27、算与人机交互/微纳信息系统微纳信息系统 第 4 页 共 4 页 ubiquitous and high-speed data access, the efforts have recently focused on improving the support of heterogeneous networks, as well as device-to device and machine-type communications. In addition to these technologies, the new paradigm of self-organizing networks ha
28、s the potential of transforming the cellular network into a dynamic entity capable of automatically adjusting itself to guarantee the best possible service by exploiting all the aforementioned technologies. This evolution will continue, not only by improving these technologies, but also by introduci
29、ng new ones, especially at higher frequency bands capable of satisfying the demand for even faster data access than the ones seen today. Cognitive radio (CR), which allows secondary users (SUs) to opportunistically utilize the frequency spectrum originally assigned to licensed primary users (PUs), i
30、s a promising approach to alleviate spectrum scarcity. In CR networks with single-antenna nodes, SUs can transmit only when it detects a spectrum hole in either time or frequency domain, so as to avoid causing harmful interference to PUs. Such schemes, however, only work when the primary system seve
31、rely underutilizes the assigned spectrum. Otherwise, the secondary system would not have adequate chances to access the wireless channel. Recent development in multiple-input multiple-output (MIMO) antenna techniques opens up a new dimension, namely space, for co-channel users to coexist without cau
32、sing severe interference to each other. Indeed, in CR networks where stations are equipped with multiple antennae, SUs can transmit at the same time as the PUs through space-domain signal processing. The nature of CR networks gives rise to several challenging issues that do not exist in traditional
33、MIMO systems. First, SUs are solely responsible for suppressing the interference they cause to PU receivers, as the primary system should not be aware of the existence of the secondary system. That is, we cannot rely on the PUs to do receiver-side interference cancellation. Secondly, SUs may not hav
34、e the luxury of knowing the channel state information (CSI) on the links to PUs, as the primary system would not deliberately provide their channel estimation to the secondary system. This imposes difficulty on transmitter-side pre-interference cancellation at SU transmitters. It is therefore necess
35、ary to revisit space-domain signal processing in the context of MIMO CR networks. In particular, SUs need to configure their beamforming patterns in a way that balances between their own throughput and the interference they cause to PUs. Due to the proliferation of various high-bandwidth application
36、s, the most benign, low frequency radio spectrum is becoming over-crowded. A natural option is to use higher carrier frequencies, such as for example millimeter-waves (mm waves) at say 60 GHz, where these high-frequency carriers have a potentially high bandwidth, but are characterized by a low wirel
37、ess propagation range. Therefore, a large number of Radio Access Points (RAPs) are required for providing seamless coverage. In order to cope with the increasing bandwidth demand per user, network operators often have to split the existing cells into smaller cells. However, increasing the number of
38、base-stations is not always a feasible option due to the higher infrastructure costs involved. One of the major access network solutions for future highbandwidth wireless communication systems is based on optical fibers for the transmission of radio signals between the Base Station (BS) and RAPs, which is generally referred to as a Radio Over Fiber (ROF) solution.
