Wireless Multimedia Systems
Spring, 2005 (HOMEWORK 1, Due Day: 9:00AM, March 16, 2005)
wmshw@wmlab.csie.ntu.edu.tw (electronic submissions)
http://inrg.csie.ntu.edu.tw/course/wms
1. At the start of 21st century, the wireless mobile markets are witnessing
unprecedented growth fueled by a information explosion and a technology
revolution. (A) Explain (1) the trend in the radio frequency (2) the trend in
the mobile network area. (B) Can you describe how mobile internet
revolutionizes the services that can be provided to consumers in the right
place and at the right time? (C) Can you explain the differences between
pervasive computing and mobile computing in terms of localized
scalability?
(A)(1)In the radio frequency arena, the trend is to move from narrowband to
wideband with a family of standards tailored to a variety of application needs.
(2)In the mobile network area, the trend is to move from traditional
circuit-switched systems to packet-switched programmable networks that integrate
both voice and packet services, and eventually evolve toward an all-IP network.
(B)Wireless mobile communications may not only complement the well-established
wire line network; it may also become a serious competitor in years to come.
(C)In pervasive computing, the density of interactions has to fall off as one moves
away; otherwise, both the user and his computing system will be overwhelmed by
distant interactions that are of little relevance. Although a mobile user far from home
will still generate some distant interactions with sites relevant to him, the
preponderance of his/her interactions will be local.
2. (A) Discuss the similarities and differences between a conventional cellular
radio system and a space-based (satellite) cellular radio system. What are
the advantages and disadvantages of each system? Which system could
support a larger number of users for a given frequency allocation? Why?
(B) Today, airplanes seem to be the last remaining islands where mobile
communications and Internet access are not available. Do you have any
solution for deploying the mobile communications and Internet access in
the airplane?
(A)
conventional cellular radio system:
(1).advantage
a.提供高行動力大範圍的雙向無線通訊
b.讓在公路上行使的車子使用
(2).disadventage
a.只能使用<0.5 瓦的傳輸功率
b.在室內會受到牆壁的阻擋
c.涵蓋範圍比較小
space-based (satellite) cellular radio system
(1).advantage
a.涵蓋範圍非常大 (遍佈全球)
b.可以提供長途旅行使用
(2).disadvantage
a.比較貴
b.只能提供相當有限品質的聲音或是資料訊息
c.室內經常會收不到而且嚴重到就算只是棵樹也可能收不到
Therefore, conventional cellular radio system could support a larger number of users
for a given frequency allocation because of space-based (satellite) cellular radio
system is too expensive for common users and its quality isn’t good enough for voice
communication.
(B)那可以使用 space-based (satellite) cellular radio system, 因為它涵蓋範圍非常
大而且可以提供長途旅行使用, 只要再飛機上架一台 Ap 接收訊號, 就可以解決
這個問題了.
3. Describe the difference between ad hoc (multi-hop) mode network and
cellular infrastructure (single-hop) mode network. Which one could be
deployed dynamically? Which one might require distributed schemes? In
your opinion, is that possible the next generation network will be
infrastructure-less, self organized networks?
(1)一個行動無線網路是利用無線電波將一群分散在各處的行動終端設備（或節
點）所組成。行動無線網路通常可區分為Single-hop 與multi-hop 二種，在
Single-hop 網路中，封包資料可直接由來源端送達接收端而不必透過中繼站點，
這可以想像成GSM 系統中手機（mobile station）與基地台（base station）間的通
訊情況；而在multi-hop 網路中，工作站間並無區別，而且封包傳輸過程可能須
經由數個中繼站點，如下圖，一個工作站收到封包訊息，然後就將它轉送（relay）
給目地端（或下一個中繼站點）
(2)由(1)所述可知multi-hop could be deployed dynamically
(3)同(2) multi-hop might require distributed schemes
(4)我覺得如果能夠達到各種介面互相轉換都沒有障礙而且成本能夠再低廉一些
的話，it’s possible the next generation network will be infrastructure-less, self
organized networks
4. Describe the difference between the first generation mobile wireless
cellular system, the second generation mobile wireless cellular system and
the third generation mobile wireless cellular system. Describe their
different user base expansion. Can you offer reasons for fast growth for the
second generation mobile wireless cellular network industry?
The first generation mobile wireless cellular system: It’s analog and based on
frequency-division multiplex (FDM) technology.
The second generation mobile wireless cellular system (2G): Digital technology
standards included Global System for Mobile Communications, IS-136, IS-95, and
Personal Digital Cellular(PDC). Digital technology has not only improved voice
quality and services, but more important, significantly reduced the cost of handset
and infrastructure systems, leading to further acceleration of the industry's growth
since the mid-1990s.
The third generation mobile wireless cellular system (3G): It will significantly
improve the spectral efficiency and possibly the cost of the system, a more
profound feature is the significant improvement of its data and multimedia
capabilities.
The reasons for fast growth for 2G industry are that: first, the industry's consumer
base was changed from the number of vehicles to the number of people, which is a
much larger base. Second, the function of the phones was also changed from being
able to call from a vehicle to being able to call from anywhere.
5. If a total of 33 MHz of bandwidth is allocated to a particular cellular
telephone system that uses two 25-kHz simplex channels to provide full
duplex voice channels, compute the number of simultaneous calls that can
be supported per cell of a system users:
(A) FDMA
(B) TDMA with 8-way time multiplexing
Assume that additional bandwidth is reserved for the control channels.
(A) 33MHz/ (25kHz*2) =660 #
(B) 33MHz/(25kHz*2)=660 660*8=5280 #
八個處理?)
(猜的 不懂 8-way 的意思 同時分成
Sols:
1. (A)
(1)In the radio frequency arena, the trend is to move from narrowband to
wideband with a family of standards tailored to a variety of application
needs.
(2)In the mobile area network, the trend is to move from traditional
circuit-switched systems to packet-switched programmable networks that
integrate both voice and packet services, and eventually evolve toward an
all-IP network.
(B)
Accompanied by wireless mobile location technology, wireless mobile Internet is
expected to revolutionize the services that can be provided to consumers in the
right place and at the right time. There are two types of geolocation techniques, one
based on the network and the other on the handset. In network-based solutions, the
geolocation information is generally estimated through the timing, arrival angle,
and strength of the signals received from handset. However, Handset-based
techniques are mainly based on satellite signals using the Global Positioning
System (GPS).
(C)
mobile computing:
Typically ignore physical distance. A web server or file server should
handle as many clients as possible, regardless of whether they are located next
door or across the country.
pervasive computing:
The density of interactions has to fall off as the user moves away; otherwise,
both the user and his computing system will be overwhelmed by distant
interactions that are of little relevance.
2. (a) The satellite-based systems, which are like cellular radio systems, is base station
systems. It also could provide limited quality voice and/or very limited data
or messaging.
The difference from cellular radio systems is that they are very
widespread coverage (often global). They are expensive, too.
Proposed satellite systems are low-earth-orbit (LEOS) systems (ten to
hundreds of satellites), medium height systems (MEOS), geostationary or
geosysnchronous orbit systems (GEOS)(fewer than ten satellites). LEOS
could provide higher capacity and less transmission delay while GEOS only
require a few (perhaps three) satellites to cover the earth.
(b)Advantage: to provide large regional or global coverage to users outside
buildings. Satellite systems can complement terrestrial cellular or PCS
systems in low population density areas.
Disadvantage:
1. Difficult to provide adequate link margin to cover inside buildings, or even
to cover locations shadowed by buildings, trees or mountains.
2.difficult to provide from earth orbit the small coverage cells that are necessary for providing
high overall systems capacity from frequency reuse.
(c)Cellular radio systems can provide small coverage cells to support a larger
number of users for a given frequency allocation. To achieve this, more
satellites are needed. Satellites are more expensive than cellular radio systems,
so it is costly to serve the same number of customers. In fact, satellite systems
are not likely to compete favorably with terrestrial systems in populated areas,
or even along well-traveled highways. It remains to be seen whether there will
be enough users with enough money in low population density regions of the
world to make satellite mobile systems economically viable.
3. (A)
There are several differences between ad hoc mode network and cellular
infrastructure. The major difference is network topology. The Ad hoc network is a
collection of wireless mobile hosts forming a temporary network without the aid of
any centralized administration. Besides, ad hoc networks are basically peer-to-peer
multi-hop mobile wireless networks where information packets are transmitted in a
store-and-forward method from source to destination. However, cellular infrastructure
means that the mobile mode must connect to one base station where the mobile node
is currently located, and base station acts as a gateway to the rest of the world. Hence,
due to the network topology, another difference is the cellular infrastructure network
can easily manage network utilization and avoid radio interference but ad hoc network
can not. Besides, routing techniques, mobility pattern, channel allocation are also
differences.
(B)
The ad hoc network could be deployed dynamically because it is an autonomous
system of mobile host (also serving as router) connected by wireless links, the union
of which forms a network modeled in the form of an arbitrary communication graphs.
The routers are free to move at any speed in any direction and organize themselves
randomly. Thus, the network’s wireless topology may dynamically change in an
unpredictable manner.
(C)
Ad hoc network also need distributed schemes. For example, the routing protocol for
ad hoc network needs dynamic, self-starting behavior.
4.
First Generation
(1G)
Second Generation
(2G or 2.5G)
Technology
Analog cellular
technology
Digital cellular
technology
Time
Early ‘80
Early ‘90
 Voice
 Data
 Fax
 Value-added
services
Voice
Transfer
capabilities
Third Generation
(3G)
 Digital
cellular
technology
 Radio
terminal
technology
Late ’90-2000
 Voice
 High-Speed
Data
 Fax
 Value-adde
d services
 Multimedia
Only a very few
Evolving with
Expected to
analog systems
remain in existence
ever-increasing data
rates via new
technologies
 GSM (Global
System for
Mobile
Communications
)

TIA/EIA-136
(Telecom.
Industry
Association/
Electronic
Industries
Alliance)
 CdmaOne_IS-95
(Interim
Standard 95)
 PDC
(Personal/Pacific
Digital
Communications
)
 HSCSD (High
Speed Circuit
Switched Data)
 GPRS (General
Packet Radio
Service)
 US-TDMA
(IS_136)
provide high-speed
data transmission
in wireless devices
 WCDMA-D
S
(Wideband
Code
Division
Multiple
Access)
 MC-CDMA
(Multi-Carri
er Code
Division
Multiple
Access)
 UTRA TDD
(Universal
Mobile
Telephone
System
Terrestrial
Radio
Access
Time
Division
Duplex)



AMPS
(Advanced
Mobile
Phone
System)
NMT
TACS
Systems
5. (A) If this system uses FDMA technology, the simultaneous calls that can be
supported per cell of a system user are
 33MHz 
  660
25KHz  2 

(B) If this system uses TDMA technology with 8-way time multiplexing, the
simultaneous calls that can be supported per cell of a system user are
 33MHz 
  8  5280
25
KHz

2

