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.