Wireless networks - Lecture 44: 4G issues

Wireless Networks

Lecture 44
4G Issues
Dr. Ghalib A. Shah

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Outline
 4G Overview
► Heterogeneous Wireless networks
► Evolution
► Issues in 4G

 Mobility Management
 Handoffs
► Types, VHO process, VHO Issues
► Standards

 QoS Considerations
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Last Lecture
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Reference Model
Burst profiles
Convergence sublayers
MAC PDU format
MAC PDU Transmission
Fragmentation / Packing
Request/Grant Scheme
Classes of Uplink service
Power management/Handoff
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4G Overview
 4G mobile communication systems tend to mean different
things to different people:
► for some it is merely a higher-capacity new radio interface,
► while for others it is an inter-working of cellular and wireless LAN
technologies that employs a variant of the Mobile IPv6 mobility
management protocol for inter-system handoff.

 There is no doubt that 4G systems will provide higher data
rates. Traffic demand estimates suggest that, to
accommodate the foreseen amount of traffic in the 2010 –
2020 timeframe in an economically viable way, 4G mobile
systems must achieve a manifold capacity increase compared
to their predecessors.

 researchers and vendors are expressing a growing interest in
4G wireless networks that support global roaming across
multiple wireless and mobile networks
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 a system that enables an “Always Best Connected” – or “ABC”


 There are many wireless network technologies
Cellular networks, Wireless LANs, Wireless
PANs, mobile Wimax, etc.
 4G networks will play a key role for integrating
various network architectures and technologies
and achieving a seamless wireless access
infrastructure
 4G provides high-speed, large volume, good
quality, and global coverage to roam between
different types of technologies
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 It is widely accepted that the individual (wireless and/or
wireline) access networks will interface to core and/or
backbone network elements over the IP protocol
 these wireless access networks are expected to have
the following in common:
► A dynamic address assignment mechanism (e.g., DHCP, SLP,
IPv6) that is capable of associating a short-lived or long-lived
IP address to the respective wireless interface at the mobile
terminal (e.g., Mobile IP COA association)
► A transparent IP forwarding service that is accessible over the

logical termination of the IP layer at the mobile terminal and
one or more gateways

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Heterogeneous Wireless Networks
 A mixture of co-existing radio access
technologies.
 Different access technologies (radio interfaces)
and overlapping coverage.
 Different network architectures and protocols
for transport, routing and mobility management.
 Different service demands from mobile users
(low-data rate, high-data rate, voice,
multimedia, etc)
 Different operators in the market.
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Evolution of 4G

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He te ro g e ne o us  Ne two rks

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Issues in 4G
 Need to resolve issues as
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Access
Handoff
Location coordination
Resource coordination to add new users
Support for multicasting
Support for quality of service
Wireless security and authentication
Network failure and backup
Pricing and billing.
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Mobility Management
 Mo bility Manag e me nt
► Location Management: enables system to track
location of mobile terminal (MT)
• Location updates and paging

► Handoff Management: the process by which an MT
keeps its connection when it moves from one point
of attachment (base station or access point) to
another

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Handoff Management
 Low signalling and processing overhead.
 Minimum packet loss and delay (seamless
HO).
 Guaranteeing QoS during the process and
transfer of context.
 Use of any “triggers” or metrics available to
decide when and where.
 Efficient use of network and MT resources.
 Enhanced scalability, reliability and robustness.
 Allow inter-technology handoff (VHO).
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Handoff Types
 Homogeneous (Horizontal) Handovers
► Within Single Network (Localized Mobility)
► Limited opportunities
► Mainly use received signal strength (RSS) to decide
handoff

 Heterogeneous (Vertical) Handovers

► Across Different Networks (Global Mobility)
► More Opportunistic
► Handoff metric: RSS, offered bandwidth, price,
power consumption, speed, …….
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Vertical handoff process
 Step 1: “System Discovery”
 Step 2: “Handoff Decision”
 Step 3: “Handoff Execution”

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Step 1: “System Discovery”
 MT must know which
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wireless networks are reachable.
Periodic beacons from AP.
Signal measurements.
Handoff metrics (network information) gathering:
Bandwidth, cost, delay, SNR, power, etc.
► Periodic network scanning.
► All interfaces always on.

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Step 2: “Handoff Decision”
 MT then evaluates the
► Some example policies:
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“Always  us e  the  che ape s t ne twork”.
“Always  us e  the  inte rface  with lowe r powe r cons um ption”.
“Always  us e  the  W LAN”.
“Always  us e  the  ne twork with m ore  bandwidth”.

► Decision may be based on utility / cost functions.

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Step 3: “Handoff Execution”
 If MT decides to perform a VHO, it executes
the VHO procedure required to be associated
with the new wireless network.

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VHO Issues

 When to switch?
► VHO policies
► WLAN to Cellular ≠Cellular to WLAN

 Seamless handoff
► Packet loss and VHO latency.

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Load balancing between networks.
QoS guarantees
Security and Authentication.
Billing
Implementation.
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Standardization Efforts
 IETF
► Mobility for IPv4 (MIPv4)
► Mobility for IPv6 (MIPv6)
► Mobility for IP: Performance, Signalling and Handoff
Optimization (MIPSHOP)

 IEEE 802.21 Media Independent Handover Group is
working toward the seamless handoffs between IEEE

802.XX family and 3G Cellular
 3GPP and 3GPP2 are working in inter-working with
WLAN as an extension of their radio access networks.
► Loosely Coupled Architecture
► Tightly Coupled Architecture
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 Tightly coupling
► Provides common charging and billing service
► Provides mobility support using traditional 3G
technology
► Reuses 3G service (e.g., SMS, MMS, etc.)
► Causes large traffic load in 3G core network

 Loosely coupling
► Provides simple integration approach
► Needs minimal requirement on the access network
► Provides independent network management
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QoS
 Supporting QoS in 4G networks will be a major
challenge due to varying bit rates, channel
characteristics, bandwidth allocation, faulttolerance levels, and handoff support among
heterogeneous wireless networks.
 QoS support can occur at the
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Packet,
Transaction
Circuit
User
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 Packe t­le ve l QoS  
► applies to jitter, throughput, and error rate.
► Network resources such as buffer space and access
protocol are likely influences.

 Trans action­le ve l QoS  
► describes both the time it takes to complete a
transaction and the packet loss rate.
► Certain transactions may be time sensitive, while
others cannot tolerate any packet loss.

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 Circuit­le ve l QoS  
► includes call blocking for new as well as existing
calls.
► It depends primarily on a network’s ability to
establish and maintain the end-to-end circuit.

 Us e r­le ve l QoS  
► depends on user mobility and application type.
► The new location may not support the minimum QoS
needed, even with adaptive applications.

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End­to ­End Qo S
 Developers need to do much more work to address
end-to-end QoS.
► They may need to modify many existing QoS schemes,
including admission control, dynamic resource reservation, and
QoS renegotiation to support 4G users’ diverse QoS
requirements.

 A wireless network could make its current QoS
information available to all other wireless networks in
either a distributed or centralized fashion so they can
effectively use the available network resources.
 Additionally, deploying a global QoS scheme may
support the diverse requirements of users with different
mobility patterns.
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QoS Parameters
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802.11e

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UMTS (Release 5)
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Nominal MSDU size
Min/mean/max data rate
Mean/max service interval
Traffic type (isochronous, asynchronous)
Burst size
Traffic class (conversational, streaming, interactive, or background)
Guaranteed, maximum bit rate
Maximum SDU size
SDU/bit error ratio
Transfer delay

802.16-2004
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Traffic priority
Maximum sustained traffic rate
Maximum traffic burst
Minimum reserved traffic rate
Scheduling type (best-effort, non-real time polling, real-time polling, unsolicited grant)
Tolerated jitter, maximum latency

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