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課程名稱︰ 無線多媒體系統研究
課程性質︰ 多媒體
課程教師︰ 吳曉光
開課學院： 電資
開課系所︰ 資工
考試日期（年月日）︰2011.06.20
考試時限（分鐘）：180
是否需發放獎勵金：是
（如未明確表示，則不予發放）
試題 :
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.
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