Introduction: Mobile and Wireless Network

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IntroductionMobile and Wireless Network
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1. Paradigm Shift to Mobile Comm.

• S-curve
• S-curve viewed from research and development
• The tool that helps to decide on whether an
  enterprise should continue the use of a
  technology or replace the technology with
  something else
• Shift to the new paradigm at the emerging era
• At a certain point the advantage of new paradigm
  suddenly increases, and the new paradigm suddenly
  settles down
• Product companys view
• Disadvantage new technology costs more to adopt
• Advantage
• To have good and renowned reputation
• More time era to sell a certain model
• Patents
• User(businessmen)s view
• Disadvantage high product cost and high monthly
  fee
• Advantage advantages coming from prompt or
  distinguished action

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1. Paradigm Shift to Mobile Comm.

• S-curve in communication (telephone) networks
• 1st generation
• Analog and mechanic and electric
• Advantage talking on the phone instead of
  running to him(her)
• 2nd generation
• Digital and electronic
• Various flexible control
• Advantage high speed data transfer, reliable and
  personalized services
• 3rd generation
• Mobile handset fixed networks
• Advantage Quick access, Low cost in setup and
  maintaining (one mobile phone acts for many
  phones, No cabling cost)
• 4th generation
• Mobile handset, mobile network

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1. Paradigm Shift to Mobile Comm.

• Pros and cons of mobile systems
• Advantages
• Convenience going to the phone ? the phone comes
  to us
• Quick access regardless ones position
• Low cost in setup and maintaining
• Disadvantages
• Limited frequency spectrum
• Complex technologies
• Quality of signals
• Power supply for the small portable units

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1. Paradigm Shift to Mobile Comm.

• Wireless mobile communication system
• Mobile station end-users can walk, or move in a
  car
• Land station(base station) the communication
  nodes are built distributed throughout the
  service area
• Communication between two mobile nodes is done
  via mobile station, and there is no direct
  communication between them
• The first commercial mobile system AMPS(Advanced
  Mobile Phone System) is implemented in 1983

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1. Paradigm Shift to Mobile Comm.

• (frequency) spectrum allocation problem
• Limited frequency (cost for use it)
• Frequency usage ratio is very important topic in
  wireless communication
• Cell reuse or spread-spectrum is known to be much
  efficient way

without cell reuse
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2. Cell Concepts

• Regular cells
• Regular cells dominant regions covered by each
  cells are all same
• There are only three regular cells triangular,
  square, hexagonal
• In N-gonal shapes, angle ? (N-2) p / N
• For regular shaping, ? should be in the form of
  2p/k where k is an integer
• The satisfying N 3, 4 and 6 only

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2. Cell Concepts

• Why we only use hexagonal units?
• Hexagonal positioning of base station is the most
  efficient
• Area of unit
• Proportional to number of base stations
  proportional to setup cost of base stations
• Number of neighbors to a single unit
• Way of hand-off proportional to base station
  networking and control complexity

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3. Transmission using Frequency Spectrum

• p. 23
• ILF voice frequency
• MF AM radio
• VHF FM radio
• UHF TV broadcasting, PCS

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3. Transmission using Frequency Spectrum

• Wireless transmission
• Electro-magnetic radiation is created, if enough
  current is loaded into an antenna
• Antenna
• Antenna length approximately the same as the
  wavelength of the generated signal
• Directed antenna most radiation is focused to a
  certain direction
• Non-directed antenna radiation is generated
  uniformly to all direction
• As frequency(v) increases,
• Smaller wavelength ? C/v (Clight speed)
• Energy increases, E hv, hPlanck constant
• Tends to proceed in straight
• More data can be inserted

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3. Transmission using Frequency Spectrum

• Type of radio waves (p. 24)
• Depending on the nature of the frequency and type
  of transmission
• Grounded or surface wave (LF, MF 30k-3MHz)
• Follows the curvature of the earth
• The long wavelength in this category is
  relatively immune to terrestrial condition (tree,
  mountain, buildings,), while the short
  wavelength is sensitive to them
• Space wave (VHF, UHF, SHF or upper 30MHz-)
• Covering more area than ground wave
• Sky wave (3-30MHz)
• Transmitted upward to ionosphere, and reflected
  back to the ground
• For radio-broadcasting and long-distance
  telephone line
• Satellite-based wave (2-40GHz)
• Upward transmission
• Downward transmission

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3. Transmission using Frequency Spectrum

• Speech transmission (p. 35)
• Voice waveform spoken into a phone creates an
  electrical alternating current
• Sound wave consists of a band of frequencies
• Spoken vowels occupy mostly the lower portion of
  frequency band
• Consonants use less power and generally occupy
  high frequency band
• Due to the difficulties in transferring speech
  signal, spectrum is cutoff in 200-3500Hz
• Low frequency FL It is hard to reproduce low
  frequency exactly using a normal speaker
• High frequency FH high frequency usually is cut
  off during transmission on electrical line
• Bandwidth B(FH-FL) is proportional to
  transmission cost
• Guard band transient part to guarantee that no
  signal generates out of given bandwidth

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4. Wireless Transmission System

• (Geo-synchronous) orbit satellite
• Satellite whose position remains fixed according
  to the equator
• 22,300 miles high from the ground (1 mile about
  1.609 km)
• Moves with the speed of 6,900 mile/h
• A geo-synchronous satellite covers 30 of the
  surface of the earth
• Microwave system
• Direct line of sight transmission
• 30-50km apart, 2-40GHz
• For wide-band transmission and radar
• Infra-red transmission system
• Using directed infra-red signal
• 1 mile distance at maximum
• High data transfer rate with relatively low cost
• Cellular radio system
• Wireless LAN

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Fundamentals of Cellular Systems
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Introduction

• Target mobile system be efficient in the use of
  limited spectrum bandwidth
• Generals
• Mobile cellular components in early cellular
  systems
• Mobile station, base station, switch station
• Wireless signal characteristics
• Multipath and its prevention
• Cell design issues
• Wireless signal distortion
• Shapes cell reuse
• Evolution of cells cell splitting, cell
  sectoring
• Roaming and handoff

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1. Early Cell System

• Non-trunk radio system
• Does not use multiplexing scheme
• Each radio channel is fixed to a specific user or
  a group of users
• Trunk radio system
• (synchronous or asynchronous) multiplexing scheme
• Channels are shared and available to all users
• Advantage increased efficiency of spectrum usage
• Disadvantage more complex architecture required

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1. Early Cell System

• Trunk radio system (AMPS) (p. 66)
• BTS (base station) controls the air interface
  between the mobile station and MTSO
• Mobile station having frequency-agile machine
  that allows to change to a particular frequency
  designated for its use by the MTSO
• MTSO responsible for switching the calls to the
  cells providing
• Interfacing with telephone network and backup
• Monitoring traffic
• Performing testing and diagnostics, network
  management functions

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2. Wireless Signal Characteristics

• Key issues of cellular system design
• Let the receivers accommodate to a wide variety
  of signal characteristics
• Use frequency efficiently
• Path loss (p. 68)
• Measured in dB(decibel) 10 log (Pr/Pt)
• In wide range decreasing as distance becomes
  apart
• In short range very fluctuating (because of
  multipath)

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2. Wireless Signal Characteristics

• Multi-path propagation
• There is little direct line-of-sight path between
  base and mobile station
• Most paths are indirect path and their total
  distance are all different
• multi-path signal
• Mixed with reflected, diffracted, and direct
  signal
• Direct signal is the strongest
• As signal gets reflected or diffracted, it loses
  considerable portion of energy
• Different distance of multipath
• Causes phase shift of signals ? think vector
  addition
• Causes multipath signal loss

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2. Wireless Signal Characteristics

• Multipath delay variation (p. 69)
• Multipath delay varies as a mobile station moves
• Time dispersion (time delay spread) get worse as
• Distance between base-station and mobile station
  increases
• Frequency becomes high

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2. Wireless Signal Characteristics

• Multi-path fading (Rayleigh fade) (p. 70)
• Definition
• Suppose signal is sent in long distance
• It creates multi-path signals
• When all kinds of multi-path are combined in
  vector addition, the signal tends to have special
  curve called Rayleigh fade
• Curve characteristics
• Good signals are interspersed with narrow, but
  very poor signals, called fade
• Signal peaks are relatively smooth
• Signal fades are very narrow, deep and totally
  unpredictable
• There is no way to predict at which position fade
  occurs in real system

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2. Wireless Signal Characteristics

• Prevention from (reduction of) Rayleigh fade
  effect ? use a pair of antennas
• At base station
• Install a pair of antennas vertically in a few
  inches apart
• At mobile station
• Install a pair of antennas one of them vertically
  and the other horizontally
• As receiving device is randomly positioned,
  vertical or horizontal line positions differently
• But these co-located antennas have very different
  reception characteristics (the fades received in
  from these two antenna are differently located)
• If two signals from two co-located antennas are
  combined, most of fade shrinks or disappears

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3. Cell Design Issues

• Frequency reuse D/R
• D the shortest distance between two cells that
  use the same frequency
• R radius of cells
• N reuse pattern number of different
  frequencies in a cluster
• For 7-cell group that has 3-mile radius cells, D
  ? 13.74 miles
• For 7-cell group that has 2-mile radius cells, D
  ? 9.16 miles

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3. Cell Design Issues

• Transmission interference
• Adjacent channel interference
• Several frequency bands are effective in a cell
• Interference between two adjacent frequency bands
• Co-channel interference
• Interference between signals of the same
  frequencies generated from or to the different
  base station
• Co-channel interference reduction factor (q)
• q D / R

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3. Cell Design Issues

• Density of mobile node/cells
• Mobile terminal is not equally distributed
• Increase of subscribers
• Required cell splitting
• Cell splitting (p. 83)
• To increase cell capacity
• Install cells in half (a little bit larger than
  half) the length of current ones
• New cell area ¼ old cell area
• New cell capacity old cell capacity
• Maximum density of subscribers in the new system
  4 maximum density of subscribers in the old
  system
• With reduced power of transmission signal in both
  mobile and base station

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3. Cell Design Issues

• Cell sectoring (p. 86)
• Use 3 directional antennas instead of a
  non-directional antenna

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4. Basic Operation of Cellular Call

• Initialization of mobile system
• Power on Power is turned off and then turned on
  in a mobile station
• Scanning It begins to scan the paging channels
• The unit monitors for signals broadcast to mobile
  stations
• Tuning It chooses the strongest(best) signal and
  locks on it
• Registering It registers its whereabouts to the
  mobile network
• Listening It keeps on listening to the ongoing
  control messages from base station
• Making a call
• A user completes to keys in telephone number
• The unit finds and selects an available frequency
• The unit sends a call request message containing
  the phone number
• The MTSO receives the message and tries to
  establish call connection to reach to another
  MTSO, normal public switched telephone network,
  or another mobile network

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4. Basic Operation of Cellular Call

• Receiving a call (in AMPS)
• While the mobile unit listening to the page
  channel, it receives a page which informs that a
  call is tried to itself
• MTSO chooses an available channel and orders the
  mobile unit to use the indicated channel
• Mobile station tunes to the directed channel and
  accepts the call
• Roaming and handoff
• A mobile station moves through a geographical
  region while talking on the phone
• MSTO notices that the current signal is not good
  enough to maintain, and decides to initiated
  handoff procedure
• MTSO seeks which cell(base station) has the
  strongest signal among cells that afford to give
  channels
• MTSO provides the roaming mobile station with a
  new channel through the chosen cells
• MTSO releases the old channel for other uses