课程名称︰ 无线多媒体系统研究 课程性质︰ 多媒体 课程教师︰ 吴晓光 开课学院： 电资学院 开课系所︰ 资工系 考试日期（年月日）︰ 2011.04.15 考试时限（分钟）： 180 是否需发放奖励金： YES （如未明确表示，则不予发放） 试题 : 1. (Wireless Mobile COmmunication) (A) By the end of the '80s, however, afvances in semiconductor technologies probided a vital boost to the cellular mobile industry. Using application-specific integrated circuits (ASICs), the size of the phone shrank to a small handset.Explain how the industry consumer base was changed from the second genaration cellular system to the third generation cellular system. (B) Describe the difference between narrowband CDMA system and wideban CDMA system. (C) Explain the possible chanllenges to move from traditional circuit switched system to packet switch programmable system in mobile network area. (D) Fixed xellular wireless technology provides a means to offer broadband access to multimedia services without requiring extensive coppoer or fiber subscriber plant. Relatively wide unused spectrum at frequencies above 20 GHZ has led to the development of fixed broadband wireless acces system operating in these bands, such as LMDS (local multipoint distribution system. Can you explain why LMDS does not turn out to be one of the major broadband solutions as ADSL? (E) In order to fully utilize spectrum resources, describe how "cognitive radio technologies" and "ultra-wideband radio" technologies share the spectrum with existing wireless systems. 2. (Mobile Radio Propagation) THe mobile radio channel places fundamental limitations on the performance of wireless conmmunication systems. THe transmisson path between the transmitter and the receiver can vary from simple line-of-sight to one that is severely obstructed by buildings, mountains, and foliage. Modeling the radio channel has historically been one of the most difficult parts of mobile radio system design, and is typically done in a stastistical fashion, basd on measurements made specifically for an intended communication systems or spectrum allocation. (A) List the factors to determine the Link Budget (SNR) (B) Describe the two main factors to cause the small-scale fading? (C) Explain the following three interference sources, in the cellular mobile system: co-channel interference, adjacent channel interference, inter-symbol interference. (D) Explain the large aread interference problem for IEEE 802.11. 3. (CSMA, MACA, adaptive CSMA, CSMA/CA Protocols) In recent years , a wide variety of mobile computing devies has emerged, including portables, palmtops, and personal deigital assitants, Providing adequate network connectivity for these devices will require a new generation of wireless LAN technology (A) Describe how CSMA protocol may cause and experience "hidden terminal" and "exposed terminal" problems (B) Karn proposed MACA as an alternative to traditional CSMA scheme. Explain why MACA might solve problem. (C) Explain the problem for MACA scheme. (D) Describe how "adaptive CSMA" scheme proposed by Intel Corporation address "hidden terminal problem" and "exposed terminal" problem? (E) Can you revise CSMA/CA protocols to address on "exposed terminal problem" ? 4. Wireless TCP porposals, Packet loss Distinction I.(A) A number of wireless TCP proposals have been proposed to address the wireless random packet loss effect. In order to distinguish congestion loss and wireless random packet loss, ECN(Explicit Congestion Notification) was proposed. Explain how ECN could function properly to avoid unnecessary TCP congestion window reduction. Describe the disadvantage of ECN scheme. (B) Explain how TCP Westwood utilized (availallbe) bandwidth estimation scheme to avoid wireless performance degradation. Describe the disadvantage of TCP Westswood. II. Future broadband satellite networks relying on GEO, MEO,and LEO constellations intend to provide a wide variety of high and medium bit-rate data services to the end user. Given that IP application in general and TCP/IP(WWW,email,file transer) more specifically are by far the most popular in the current data networks, it becomes quite evident that TCP will be the transport protocol of a significant part of the traffice of all networks including satellite networks. (C) For typical Satellite Networks with long propagation delays and hihg link error rates, explain the possible adverse effects of TCP Reno. (D) Propose and end revison solution of TCP Reno to address the adverse effects. 5. Network Mobility Consider vehicles such as ships, aircrafts and trains that contain mobile networks with a potentially large number of devices requiring gloval connectivity. These devices may or may not be sophisticated nodes. By employing a special entity namely a Mobile Router to act as a gateway, all devies with the network can achieve global connectivity irrepective of their capabilities. NEMO working group identifies 3 types of nodes that woild be supported by a mobile router. Local Fixed nodes, i.e., nodes which belong to the mobile network and cannot move with respect to the mobile router, would typically not be able to achieve global connextivity without the support of the MR. There could also be nodes which can move with respect to the MR namely Local Mobile Modes(home link belongs to Mobile Network) and Visiting Mobile nodes (home link does not belongs to Mobile Network). Describe your solution to extend "mobile IP" to support local fixed nodes, visiting mobile nodes and visiting network. -- Nothing is Impossible --

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