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The Propagation Factor in Mobile Wireless Networks

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Title: Application Requirements Author: Syed Abbas Last modified by: SABBAS Created Date: 5/24/2000 9:07:52 AM Document presentation format: On-screen Show – PowerPoint PPT presentation

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Title: The Propagation Factor in Mobile Wireless Networks


1
The Propagation Factor in Mobile Wireless
Networks
  • Syed Aun Abbas
  • LUMS SSE

2
Structure of the Talk
  • Aims to look at Mobile networks from numerous
    perspectives
  • Business considerations
  • Inter cell considerations
  • Intra cell considerations
  • System considerations
  • The focus is to understand issues and design
    considerations
  • Identify issues that still need attention and
    could form basis for future research

3
Business Considerations
  • Mobile operators own limited Bandwidth and
    limited Transmission Power.
  • They pay heftily for these resources
  • Want to sell services to the customers
  • Typical Services/Applications
  • Voice
  • Data
  • Real/Non-real time Video
  • Application Requirements are
  • 1. Data Rate
  • - symmetric or asymmetric
  • 2. Latency ( delay)
  • 3. Bit Error Ratio

4
Business Considerations
  • Systems need to be designed to transform
    bandwidth and power in bits/sec of voice video
    and data that meets latency and bit error
    requirements
  • Do it in a manner that number of customers who
    can use these resources for payable applications
    should be maximized.
  • There are different dimensions to the last
    statement
  • Design a system that provides maximum useable
    bits per second for the whole system
  • This maximum capacity should be available to the
    subscriber base
  • A lot many time this capacity is not usable by
    the customers
  • Researchers continually try to find ways and
    means to improve upon system capacity and its
    utilization
  • Message to take home System capacity is nearing
    limits but is utilization too?

5
INTERCELL CONSIDERATIONS Maximizing Capacity of
the Mobile Systems
  • How can we achieve the objective?
  • Use Frequencies repeatedly
  • Use Digital Communication
  • Allows Compression
  • Allows easier multiplexing of the different
    tribes of services
  • Triple play gt Voice/Data/video
  • Use Intelligent Control Techniques
  • Dynamic Channel Assignment uses resources smartly
  • Use Trunking

6
INTERCELL CONSIDERATIONS Cellular Concept Use
Frequencies repeatedly
7
INTERCELL CONSIDERATIONS Frequency Reuse -
Cellular Concept
  • System capacity is co-channel interference
    limited
  • Carrier-to-Interference ratio (C/I) is the
    parameter of interest
  • Isolation derives from distance between cells
    using the same frequency group
  • Frequency planning
  • Split total bandwidth in N sets of k channels
    each
  • Allocate one channel set per cell without gaps
    and repeat
  • N increases, so does D and co-channel
    interference decreases
  • N increases, the number of channels per cell
    decrease and so does the system capacity
  • Problem is to find an optimum layout for an
    initial service that should be able to scale as
    system usage changes

8
INTERCELL CONSIDERATIONS Frequency Reuse
Scaling the network
  • Cell splitting
  • Reduce antenna heights and transmit power
  • Do not upset the channel assignment scheme
  • Do not upset the SIR
  • Generally, reduce the radius to half
  • Practical implications remain
  • More handoffs,
  • CELL SECTORING
  • Use directional Antennas Propagation can be in
    120 or 60 degree sectors
  • Sectoring improves SIR by reducing the
    interference
  • More handoffs, however, as long as Base station
    handles handoff, MSC may be spared
  • Trunking efficiency may be reduced

9
INTERCELL CONSIDERATIONS Frequency Reuse
Scaling the network
  • CELL ZONING gt Kind of distributed base station gt
    Still under active considerations
  • Addresses Trunking Inefficiency in Cell Sectoring
  • While 10 trunked channel with 0.01 GOS can
    support 4.46 Erlangs of Traffic, 2 groups of 5
    trunked channels support 2.72 Erlangs of Traffic
  • Conclusion It is desirable to have smaller
    cluster sizes with more channels/cell to maximize
    capacity
  • Any base station channel may be assigned to any
    zone
  • Making zones in a cell reduces the R in D/R and
    thus increases D/R while reducing Tx. power of
    the Cell
  • Radio Channel Assignment
  • Dynamic vs. Fixed
  • Fixed Channel Assignment Calls blocked when all
    channels in use
  • Dynamic Channel Assignment does not allocate
    channel for cells permanently
  • Dynamic channel allocation takes into account
    likelihood of future blocking in the cells, the
    frequency of use, the reuse distance of the
    channel and other cost functions
  • Requires real time data on channel occupancy,
    traffic distribution and radio signal strength
    indications

10
INTRACELL CONSIDERATIONS Maximize
bits/sec/user/GPS coordinate
  • Transceiver Design Issues
  • Transmit Signal Design - BW, Framing, Data Rate,
    Modulation
  • Signal Receiver Design - Coding, Interleaving,
    Diversity, Equalization etc.
  • All of the above have implications on how the
    radio waves are received at the receiver and what
    kind of issues are associated with them.
  • Signal Propagation Issues
  • Path Loss Prediction - Large Scale Issues gt
    Determine the receive signal strength
  • Other Channel Impairments Fading, Doppler
    Frequency Shift and Delay Spread - Small Scale
    Issue
  • We know what are characteristics of the ideal
    transmission channel. Same loss at all
    frequencies and linear phase charter.

11
INTRACELL CONSIDERATIONS Received Radio Signal
at a Mobile
  • It has loss and variability in the loss

12
INTRACELL CONSIDERATIONS Signal Propagation -
Path Loss
  • Mobile cellular environment
  • Outdoor Environment
  • Macro, Micro and Pico Cells
  • Indoor Environment
  • Pico cells
  • Propagation Mechanism in Real Environments
  • Multipath Propagation
  • Reflection
  • from the ground, building walls etc.
  • Reflection coefficient
  • Refraction
  • through walls etc.
  • Diffraction
  • because of edges of the buildings, hills etc.
  • Scattering
  • because of Rough reflecting surfaces

13
INTRACELL CONSIDERATIONS Different types of
Fading and transmission rate/reach limitation
Symbol duration, T
FAST SELECTIVE
FAST FLAT
Tc
SLOW SELECTIVE
SLOW FLAT
Signal Bandwidth
Bc
14
INTRACELL CONSIDERATIONS
  • From where all these impairments come from
  • Physics and environment geometry
  • Multipath propagation is the culprit (or hero in
    some cases e.g., MIMO)
  • How can we get rid of these environments?
  • Can we really?

15
YES
16
INTRACELL CONSIDERATIONS
  • Yes! WE CAN
  • Antennas with adaptive beam forming can help
  • If we can reduce the beam width sufficient small
    it virtually becomes free space path loss, fading
    due to multipath vanishes ISI due to multipath
    vanishes,
  • MIMO will not yield gains anymore But do we need
    them anymore?

17
Modulation and other radio interface are barely
any different
18
SYSTEM CONSIDERATIONS RF Coverage Optimization
Issues Remain Automate them further
  • Focus Cell power resources where the users are
  • Know the location of your users
  • Know the spatial distribution of the users
  • Know the temporal distribution of users per beam
    footprint
  • Beams should follow users temporal movement
  • How do we get the information from the users
  • Architectural and legal issues
  • Give rise to a new paradigm
  • May need overlaid open network management
  • How to ensure timely delivery with reliability?
    May need a complete new approach

19
SYSTEM CONSIDERATIONSMobile Network
Architecture GSM Networks
HLR
VLR
PSTN
AC
Um
MAPn
Voice
EIR
MS
Abis
MAPn
BTS
A
ISDN
MS
Voice/ Data
MSC
BSC
HLR- Home Location Register VLR - Visitor
Location register MSC - Mobile Switching
Center BSC - Base Station Controller BTS - Base
Transceiver Station AC - Authentication
Center EIR - Equipment Identity Register
Data
BTS
Internet
20
SYSTEM CONSIDERATIONS GSM System - Protocol
Architecture
Base Station System - BSS
MS
BTS
BSC
MSC
CM
Q.931 ISUP TUP
MM
DTAP, BSSMAP
CM
BSSMAP, DTAP
SCCP
SCCP
MM
RR
BTSM
MTP3
MTP3
RR
BTSM
MTP3
LAPDm
LAPD
MTP2
MTP2
LAPDm
LAPD
MTP2
TDMA
T1/E1 or L1
MTP1
MTP1
TDMA
T1/E1 or L1
MTP1
Um
Abis
A
MAPn
To from other MSCs and networks
To from other MSCs
21
3rd Gen. Mobile Networks - IMT 2000
MS
BTS
BSC
MSC
CM
BSCM
SCCP
BSM
CM
BSM
CM
MTP3
CM
RR
BSM
MM
RELAY
RR
Q.2140
RELAY
LAC
Q.SAAL
LAC
LAC
Q.SAAL
Q.SAAL
LAC
TDMA
AAL/ATM/PHY
PHY
AAL/ATM/PHY
AAL/ATM/PHY
PHY
Um
Abis
A
MAPn
To from other MSCs and networks
APPLICATION
To from other MSCs
MAP(HLR)
TCAP
TCAP - TCP/UDP Convergence
SCCP
MTP3
Q.2140
TCP
UDP
Q.SAAL
IP
AAL/ATM/PHY
PHY
HLR
22
SYSTEM CONSIDERATIONS 4G LTE IP basedSystem
Architecture
23
  • THANKS and GOOD LUCK

24
ABSTRACT
  • The mobile communication services market is now
    focused on delivering data services which have
    come a long way from short messaging and paging
    services. WiMax and LTE are leading contenders to
    proliferate the mobile data networks market. With
    most of the technology feature being very
    similar, the winning attributes of the two
    technologies are not related to their own
    technical virtues but are elsewhere. In this
    talk, we would provide a perspective on how
    propagation plays a significant role in that
    determination. We would also attempt to identify
    some areas of continuing research that should be
    most useful to impact the future of mobile data
    networks.
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