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 开课系所︰ 资工 考试日期（年月日）︰2011.06.20 考试时限（分钟）：180 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题 : 1. Digital Newtowrk Coding for wireless mesh networks Consider the canonical example for wireless network coding shown in Fig 3 (a). Alice and Bob want to send a message to each other. The radio range does not allow them to communicate without a relay. In traditional 802.11, Alice sends her packet to the router, which forwards it to Bob, and Bob sends his packet to router, which forwards it to Alice. Thus, to exchange two packets, the traditional approach needs 4 time slots. Network coding achieves the same goal, but with fewer time slots. In particular, Alice and Bob send their packets to the router, one after the other; the router then XORs the two packets and broadcasts the XOR-ed version. Alice recovers Bob's packet by XOR-ing again with her own, and Bob recovers Alice's packet in the same way. Thus, network coding reduces the number of time slots from 4 to 3. The freed slot can be used to send new data, improving wireless throughput. (A) Describe the advantage and disadvantage of Digital Network Coding. (B) Design a QoS routing scheme by properly exploiting digital network coding for wireless mesh networks (WMNs). 2. Analog Network Coding for Wireless Mesh Networks Traditionally, interference is considered harmful. Wireless networks strive to avoid scheduling multiple transmissions at the same time in order to prevent interference. This paper adopts the opposite approach; it encourages strategically picked senders to interfere. Instead of forwarding packets, routers forward the interfering signals. The destination leverages network-level information to cancel the interference and recover the signal destined to it. The result is analog network coding because it mixes signals not bits. So, what if wireless routers forward signal instead of packets? Theretically such an approach doubles the capacity of the canonical 2-way relay network. Surprisingly, it is also practical. (A) Describe the advantage and disadvantage of Analog Network coding. (B) Design a QoS routing scheme by properly exploiting analog network coding for wireless mesh networks (WMNs). 3. IEEE 802.16 The broadband wireless access industry, which provides high-rate network connections to stationary sites, has matured to the point at which it now has a standard for second- generation wireless metropolitan area networks. IEEE Standard 802.16, with its WirelessMAN air interface, sets the stage for widespread and effective deployments worldwide. (A) Describe how IEEE 802.16 protocol enables dynamic bandwidth allocation to math the current channel condition. (B) Describe and explain the downlink sbu-frame structure and uplink sub-frame for IEEE 802.16. (C) Describe the procedures of channel acquisition and initial ranging and negotiation of SS capabilities. (D) Describe how IEEE 802.16 could accommodate CBR (such as VoIP) and VBR (such as Video over IP) services? 4. OFDMA Considerable discussion in the wireless industry has focused on the relative benefits of TDMA, CDMA, and, more recently, OFDMA. Today, people are asking whether Orthogonal Frequency Division Multiplexing (OFDMA) and OFDMA provide any inherent advantage over TDMA or CDMA. OFDMA is currently a favored approach under consideration for radio systems that have exztremely high peak rates. OFDMA also has an advantage in that it can scale easily for different amounts of available bandwidth. This in turn allows OFDMA to be progressively deployed in available spectrum by using different numbets of subcarriers. (A) Explain how OFDMA scheme addresses on multipath interference and simplifies channel equalization (B) Explain how OFDMA adopts cyclic prefix (CP) to avoid ISI effects? (C) Can WCDMA adopt cyclic prefix approach to improve the throughput? 5. Session Initiation Protocol The Session Initiation Protocol (SIP) provides advanced signaling and control functionality for a wide variety of multimedia services. (A) Explain why and how SIP could support personal mobility. (B) Exlpain how caller could influence can influence the routing of the SIP message. (C) Explain how SIP could support forking function? (D) While alomost all phone calls are between two parties, signaling also would be required to accommodate multiparty calls (such as "PUSH TO TALK"). Describe how SIP could be enhanced to support multiparty calls. (E) Explain the motivations for IP multimedia subsystem (IMS) from the network operator perspective? (F) Describe the application-level registration and session setup in the IMS. (G) Explain the usage of PRACK (Provision response acknowledgement) message. -- 没有不可能的事, 只有不愿做的事 --

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